Developing mathematics curricula

Case Study Two: Transformation Geometry
The curriculum for transformation geometry is similar in spirit to that for integers. The students
are asked to create the objects of the subject matter, to relate them, and to construct operations
upon them. However, the structure of the subject matter in transformation geometry differs
qualitatively from that in integers. The objects are more numerous, and their composition is more
complex. Therefore, the relationships among the objects and the operations upon them are more
difficult for students to construct than is the case with integers. The curriculum reflects this.
Objects
The objects within transformation geometry are rotations, translations, and reflect ions (“flips”).
Each is to be. in the students‟ thinking, a mapping of the plane onto itself by the criterion that the
images of points remain the same distance apart as were their preimages. Rotations, translations,
and flips are special cases of this definition.
• A rotation is a mapping of the plane that leaves all points equidistant from a given point.
• A translation is a mapping of the plane that makes all segments joining images and preimages
parallel.
• A flip is a mapping of the plane that leaves images and preimages equidistant from a given line.
I have found that as characterizations of the intended objects in students‟ thinking, the preceding
are too facile and too powerful. They are too powerful in that most of transformation geometry
can be constructed from them; they have far-reaching implicat ions that are uncovered only after
a great deal of elaboration. They are too facile in that students can “record” them as
verbalizations, and yet fail to understand them in terms of anything resembling an operational
structure.
The cognitive objectives of the curriculum are transformations of figures in a coord inate plane.
In terms of the schematic in Figure 1, transformations of a figure are at Level I. The
transformations serve to connect “states” of a figure, where a state is determ ined by some welldefined criterion. A stare can be at, or between, two levels in a stud ent‟s understanding: it can be
a perceptual image, on par with any object in the stud ent‟s field of vision, or it can be a list of
property values. The properties used in the curr iculum are (1) the figure‟s position in a
rectangular coordinate plane, (2) irs heading within a polar coordinate system, and (3) its
orientation (each determined by an app ropriately well-defined method).
As a connection between visual states of a figure, a transformation is nothing more than the

students‟ estimate of the effects upon the figure of performing a physical relocat ion. As a
connection between property values of a figure, a transformation is a multivariate mapping. The
latter is clearly the more formal of the two, in that once students have the means to predict the
effects of a transformation upon a figure‟s propert ies, they have in essence developed a system
in which they can consider possibilities regardless of whether or not the figure is in their field of
vision, and regardless of whether a figure has even been specified. That is, it is only in the case
of the latter that a transformation in the students‟ thinking approximates the idea of a
transformation bei ng an isometric map of the plane onto itself. The mapping formally preserves
perceptual structure.
I should point out that the creation of a system in which my students may predict the effect of a
motion upon a figure‟s properties has been extremely difficult for them. One reason for this. I
believe, is that they have difficulty equating a particular figure in the plane with an instantiation
of the variable list [figure (position heading orientation)].
Put another way, students appear to consider a transformation at first as being app lied to, and
only to, that figure that is currently in their attention, and not to the class of congruent figures of
which the current one is only representative. They do not look at a figure as a variable. Thus, for
the curriculum for transformation geometry to emphasize transformations as objects, it must first
emphasize the states upon which transformations operate as variables. This was not apparent in
the curriculum for integers, as the college students in my courses thought naturally of position as
a variable value. It is quite possib le that middle school students will not.
One could snake a case that the ontogeneses of variables and functions are inext ricably linked,
as did Piaget et xl. (1977). If that were the case, the implication would seem to be that
instructionally the two are inseparable. From another perspective, however, they are separable—
to an extent. To bring the students to a level where, to them, the states upon which a
transformation operates are objects in and of themselves, one might ask them to build concreteoperational action schemata for the transformat ions, indirectly placing the stares into the realm
of possibilities. At least then it would make sense to them to speak of a transformation
independently of any particular state of the figure being transformed.
The genesis of transformations in the plane as mathematical objects can now be supp osed to be
(1) action schemata of physical displacement, (2) formalization of variable
figures (both within and across equivalence classes of figures, (3) transformations as functions

between lists of property values of a class of figures, and (4) transformations as isometric
mappings of the plane.
Operations
The essential operation upon transformations in the plane is composition. The genesis of
composition is supposed to be (1) coexecution—doing one transformation (of any state), doing
another (of any state). and differentiating between the two; (2) cons ecutive execution—doing
one transformation and then doing another upon the state resulting from the first; and (3)
composition—the result of consecutively executing two transformations being taken as a
transformation in and of itself. Note that the genesis of transformations as characterized here
assumes the complexity of the genesis of transformations as mathematical objects.
Milieu
As with the integers curriculum, the objects and operations of transformation geometry arc
supposed to exist within the students‟ emerging abilities to compose transformations, construct
operations, and apply operations recursively. As always, this supposition is made with the
assumption that the students‟ experiences include solving problems in which, to them, these
abilities are demanded.
Micro wo rid
The transformation geometry microworid. called MOTIONS, has as its initial display a picture of
a Cartesian coordinate system and a flag standing upright on the origin (Figure 8). The flag lies
within two frames of reference, the Cartesian coordinate system and the polar coordinate system.
It thus has several properties that serve to uniq uely identify it—its heading (the direction that the
turtle is pointing as it sits waiting for a command from the keyboard), its position (the position
occupied by the turtle), and its orientation (the direction that the turtle turns when constructing
the flag).
Other properties for which the program maintains values, but which are redundant with the
above three, are the flag‟s distance from the origin (measured from the turtle); the measure of the
angle formed by the turtle, the origin, and the positive x-axis; and the turtle‟s x- and ycoordinates. Even though these are redundant, it is pedagogically useful to have them
maintained.
As a note, the students are not limited to operating upon the figure initially supp lied by the
program; they may define new figures at will. The pedagogical utility of the capability to define

new figures will be discussed in the section Symmetries of Plane Figures.
The transformations initially supplied to the students are translations, rotations about the origin,
and flips through lines that pass through the origin. The microworld works as follows: The
student enters a command, or sequence of commands, and then the program executes it. For each
command, a flag is drawn according to the command‟s effect upon the flag‟s properties.

Figure 8. Initial display of MOTIONS. Slashes on axes are in increments of O turtle-steps.
Information given in information 1ine the flag‟s (turtle‟s) position, heading, and the measure of
the angle formed by the turtle, the origin, and the positive x-axis.
To rotate the flag about the origin, the student enters R <number>, where <number> is the
measure of the angle through which to rotate it (Figure 9). To translate the flag, the student
enters T <numberl> <number2>, where <numberl> is a distance to move and <number2> is the
heading in which to move it (Figure 10). To flip the flag, the student enters F <number>, where
<number> is the heading of the line passing through the origin through which the flip is to be
made (Figure 11).
A number of other commands are available to the students for “housekeeping” (e.g.. dearing the
screen) or for pedagogical purposes. The full glossary of commands, operations, and maintained
variables for MOTIONS is given in the Appendix of this chapter.
Curriculum
Each student is given a copy of the MOTIONS program and a copy of a module that contains
activities for them to do and questions for them to consider. In its current form, the module is
separated into five sections: Getting Acquainted, Investigations, Sym metrics of Plane Figures.
Systematic Investigations, and General Motions. In the discus. sion of each section, 1 will refer
to translations, rotations, and flips as motions, since that is the generic term used in the module.

Figure 9. Example of a rotation. Flag started at (50 20J with heading 45 and orientation „RT.
Student entetedR 50; the flag ended at (16.8 51.2J with heading 95 and orientation RT.
Figure 10. Example of a translation. Flag started at (—100 —30) with heading 120 and

orientation “RT. Student entered T 100 45(100 turtle.steps in a heading of 45 degrees); the flag
ended at [—29.3 40.7) with heading 120 and orientation „RT.

Figure 11. Example of a flip. Flag started at 1—29.3 40.7) with heading 120 and orientation “LT.
Student entered F 70 (flip through the line passing through the origin with a heading of 70). Flag
ended at (48.6 12.3) with heading 20 and orientation “RT.
Getting Acquainted. In this section, the students are informed of the screen, the information line,
and how they should read the screen. They are introduced to the conventions of polar and
rectangular coordinate systems, and to the idea of heading (equivalence class of rays). There is
usually quite a lot of discussion about heading, as students typically fix upon the origin as the
endpoint of any ray. Their fixation upon the origin leads to inordinate difficulties when they
come to heading as a parameter of a translation.
The activities in the Getting Acquainted section are designed with two aims in mind—that we
have occasions to discuss the idea of any flag being only one of an infinite number of
possibilities, and that the students internalize the motions, that is, construct schemata whereby
they can give visual estimates of the effect of a motion upon any part icular flag. By “estimate” I
mean that the students predict what they will see on the screen as a consequence of commanding
the flag to move by a particular motion.
The activities that focus on the idea of the flag as a variable have the students use the GOTO
command to make the flag appear on the screen as it does in a diagram in the module. The
parameters of GOTO are the flag‟s x- and y-coordinates, its heading, and its orientation. The
assumption is that in their examination of the pictures, the students differentiate their “flag”
schema so chat position, heading, and orientation are variable values in it. That is, the aim is that
they see any particular flag as an instantiation of its formal properties. I must point out that these
activities by themselves are not sufficient to accomplish that aim, nor are they expected to. It has
been my experience that most students do not formalize the flag until they develop schemata for
transformations of it. More than a few never formalize it.
The activities directed toward having the students internalize each of the motions are similar to
those for formalizing the flag. Students are presented with pictures to create (Figure 12), where
the means of creation is restricted to using the three motions. The kind of thinking aimed for is:

The flag is here and I want to get it there. Which mot ion should I use? What values shall I put
into it? It is hoped that in deciding upon what needs to be done to a flag in order to generate a
picture, the students will separate the motions from one another by the effects they have upon the
flag‟s properties.

figure 12. Pictures for the student to create using rotations, translations, and/or flips.

As an aside, I have found that in class discussions my use of the definite article with „flag” often
has a very different meaning for me than it has for my students. When I speak of „the” flag. I
normally mean the equivalence class of “particular” flags. Through the beginning of the
curriculum, when students use the definite article, they are normally referring to a specific visual
image. Our differences in significance became most apparent when we were discussing the
general effects of a motion upon the propert ies of the flag. I was speaking of „the” flag. when
from their perspective, sometimes there were many flags and sometimes none. It took some time
before we sorted this diff iculty out. Afterward, I revised the module so that it directly addressed
the notion of the flag as a variable.
Irn‟esr;galioiss. This section contains two distinct sets of activities and questions. The fuxt
focuses on motions as mappings between properties of the flag—that is. at this point in the
curriculum the emphasis is on the initial development of motions in the plane as transformations
of states. The second set of activities and questions focuses on composition as an operation upon
motions. It is in the second set that the students are asked to create a motion as an object in and
of itself.
The following are examples of activities and questions that focus on a motion as a mapping
between states of the flag.
1. Do each of the following and fill in the table.
(Figure 13 shows the displays that a student would see.)
2. Complete this statement: If the flag‟s heading is x, its heading after doing Ry will be_.
3. Do CLS R 670. Does the flag‟s new heading agree with your generalization in 2?
4. Do CLS F 45. The result looks like a rotation by —90 degrees. Is it?

Figure 13. The display as a student does successive rotations. First rotation is R 40; second is R
70;
thirdisR-180. Srudenrsaretoabstract(1)theeffectofRx uponthcheadutgofthcfiag, and(2)
that the flag remains the same distance from the origin. (Continued on next page.)

Figure 13. Continued
5. Do (GOTO 80 20 90 „RD Q. Ri‟. Now fill in the following cable. Precede each flip with
GRP.4
(Pigure 14 shows the displays that a student would see.)
6. The initial heading of the flag was 40. Someone entered F_. The flag‟s heading ende d up
being 110. What was the flip‟s heading?

figure 14. The display as a swdern does successive flips (each flip is performed upon the flag
with properties((8020J90 “RT).ThefintflipisP4o;thesecondisF7O;rhethizdisPlOO.Studcnts are to
abattact (1) the effect of a flip upon the flag‟s heading and orientation, and (2) that the segm ent
formed by any point and its image is bisected perpendicularly by the line of the flip.
figure 14. Continued.
7. Give a sequence of motions that will take the flag from position A to position B.
Predictions of the effect of a motion on the flag‟s position are not stressed, except in very simple
situations. To make predictions in general would require a background in trigonometry, which
these students typically do not have.
The following problems aim at having the students separate a motion from its operand, and at
having them abstract the properties of a motion per se. These problems usually prove difficult for
students. This appears to be because they must consolidate the details of a motion into one unit,
which requires a great deal of reflection. That is, they must separate the action of mentally
carrying out a motion from the experience of applyi ng those actions to a particular flag.
Apparently. the schema formed from such abstract ions is at a pseudooperative level, as it is not
bound to any particular image (visual or mental) or to a flag. However, they must still understand
that a figure is being transformed and that it has a position, a heading, and an orientation.

8. Clear the screen.
a. DoR 30R60.NowdoR9O.
6. Compare the two results of a. How are they different? How are they the same?
c. Do (GOTO —50 —70 120 “LT) CL. Do R 40 R 35. Now do R 75.
d. Compare the two results of b. How are they different? How are they the same?
9. What motion is [R 20 R 80]? How is it related to R 20 followed by R 80?
10. Complete this statement: [R x R y] — —.
11. What translation is
a. [T60270T800]?
6. [T3osoT4ol7o]?
c. [TsooT8o9o]?
12. Predict the effect of [T 80 45 T 60 0]. Test your prediction. Does the result of your test agree
with your expectation? Why?
.13a. Do CI.S. Now do T 60 160 T 40 —50. (See Figure 15.) What translation will take the flag
back to its starting position?
6. Do (GOTO 80 —50 45 “Li‟) CL. Now do T 60 160 T 40 —50. (See Figure 16.) What
translation will take the flag back to its starting position? [Hint: Refer to a.]
14. Do DEF “TWO.FLIPS [[X Y) F :X F :Yj. (See Appendix for a description of the DEF
command.)
a. What does TWO.FUPS do?
6. Test TWO.FLIPS with various inputs. What kind of motion is TWO.FLIPS?
c. Complete this statement: TWO.FLIPS x y —.
d. What is the effect of [F x TWO.FLIPS y a]?
15. The flag was taken from state A to state B by [F 40 T —100 120 F 30 R 70). Write a
sequence of motions that will take the flag from state B to state A.
The reader should note the use of brackets in the above questions. Whenever you enter a
sequence of commands on a single line. MOTIONS carries them out one at a time, just as it
would were they entered separately. In other words, MOTIONS shows the effect of each motion
upon the flag that is currern at the time of its execution. If the seq uence is enclosed in brackets,
however. MOTIONS shows only the result of the composition of the sequence. In other words,
enclosing a sequence of motions within brackets signifies the composition of the sequence.

Each of the activities and questions in the preceding group of problems fits with the general aim
of promoting students‟ reflection of the actions of carrying out a motion to a level of operativity.
Perhaps an anecdote will be illustrative.
I was working in my office one evening when two students literally banged on my door. They
wanted to share a discovery. They had been working problem 14d and quickl y decided that
since they knew that the net effect of TWO.FLIPS is a rotation, they would focus upon the net
effect of F x. After they eruered a flip on the computer, and stared at the screen for a number of
minutes. it dawned on them that the net effect of a flip is a ffip. This is the discovery that they
wanted to share. That a flip is a flip.
I cake their discovery (and to them it was a discovery> to mean that up to that point they had
looked at finding net effects much in the same way that young children look at finding sums.
There was the first motion, the second motion, and the result—three separate and distinct
entities. What these students discovered. I believe. is that the net effect (composition) of two
motions is those two motions, but in combination. That is. I believe that what they discovered
had nothing to do with flips. Rather, they created (at least for a time) a composition as an object
in and of itself, but one that has an interior,
Symmetries of Plane Figures. There are two reasons for including a study of symm etry in the
curriculum. The first is that the investigation of symmetries of plane figures provides a natural
occasion to discuss sets of motions that are closed under composition. The second is that it
provides an opportunity to pose questions that aim at having the students generalize their concept
of a motion in the plane.
16. EnterFIG[ PU FD BOLT S4 PD REPEATS I LT 72 FD 94.02] J.
This defines a regular pentagon centered at the turtle. (See Figure 17.)
a. Enter CLS.
(1) List the inputs to K that will resuk in the figure coinciding with itself.
(2) ListcheinputsroFthatwillresultinthefigurecoincidingwithitself.
1. Enter(GOTO 00 100 “RI‟) CL.
(1) Answer 16a(1).
(2) Answer 16a(2).
Students typically answer question 16a without considering that their answers assume the figure
to be in its home position, and are surprised when their answers no longer work for the figure in

a non-home position. They are equally resurprised when they find that in 16b they end up giving
the same answer for rotations as before, but diff erent answers for flips.
17 a. Define a motion, called F.SYM. for which the inputs that you listed in 16a(2) will make the
figure coincide with itself (assuming that the turtle is on the origin).
b. Define a motion, called R.SYM, for which the inputs that you listed in 16a(l) will make the
figure coincide with itself, regardless of the figure‟s position and heading.
Most typically, question I 7a is answered
DEF”F.SYM[[X]F:HDG + :X].
The most typical answers to 17b are
DEF „R.SYM [ [X] (T -:DIST :ANGLE) (R ;X) C :DIST :ANGLE)J,
and DEF “R.SYM [[X] Cr —:XCOR 0) („F —:YCOR 90) (R :X) (T :XCOR 0) cr YCOR 90)].
The following questions focus upon aspects of symmetries in a more general context than did
Problem 16.
ISa. The motions Ml, M2, M3, and M4 each make a figure coincide with itself. Will Ml M2 M3
M4 I make the figure coincide with itself? Why?
6. A figure is coincident with itself under each of F 40, F 80, and F 120. What might the figure
look like? What is the minimum number of sides in such a figure?
c. Suppose that someone tells you of finding a figure for which R 180, F 45, F 90, and F 135 are
the only motions under which the figure is symmetric (assuming it is at the origin). Do you
believe it? Why?
The questions in 18 are the fixst in the curriculum that begin to focus on the formal properties of
motions in the plane. In 18a the students are asked to think strictly in terms of possibilities.
Typically, those who have not objectified motions in the plane (as ind icated by their
performances in other contexts) either will not know how to approach the question, or will
answer it in terms of a specific example. For 18b they will try to cons truct various figures, and
then test them against the requirements stated in the quest ion. As far as I can tell, question 18c is
accessible only to those who have built an operat ional structure, for it requires a determination
of impossibility. For instance, if F 45 and F 90 are symmetries of the figure, then [ F 45 F 90 1 =
R 90 mass be a symmetry of the figure. Therefore no figure can be symmetric under just those
motions.
Systematic Investagalions. The previous sections aimed at having the students create motions as

objects in and of themselves, and at having them create composition as a binary operation upon
motions. The Systematic Investigations section aims at their coalescence of motions in the plane
into sets that have intrinsic algebraic structures. Again, the focus is on reasoning formally about
sets of motions—reasoning about possibilities. Problem 19 is an example of questions in this
section.
19. Find two sets of motions, each with four elements, that form closed addition tables.
Invariably, some students come up with R 0, R 90, R 180, and R 270 as one set, while others
come up with R 0, F 0, F 90, and R 180 as another. i count on someone coming up with
something Iske RU, F 45. F 135. and R 180 so that Ican ask if this set is different enough from
the second to count it as a different set of motions. Essentially. the subject of the discussions ii
isomorphism. To emphasize the point, I ask the students to characterize all sets of motions that
have four elements, two of which are flips, that form a closed addition table. As an additional
challenge. I ask them to try to find two different sets of motions, each with five elements, that
form a closed table. There is. in actuality, only one. The real aim of the question is for them to
find this our.
Generalized Molion.i. This last section aims at a synthesis of the students‟ various ways of
thinking about motions in the plane—as mappings between properties of a figure. as objects to
operate upon, and as elements in algebraic structures. The cornexr of the questions and activities
in this section is the problem of how to generalize the mot ions supplied by the microworid so
that it will perform rotations about any point in the plane, and perform flips through any line in
the plane (Figure 18).) will not discuss this section or the students‟ difficulties with it at any
length. I will just note that it is only after solving the problems of defining a general rotation and
a general flip that they come to think of motions in the plane as point mappings, and that they are
truly sur• prised when all of the generalizations that they have made up to this point continue to
hold as special cases for motions in general. Apparently, even when working abstractly with
motions, they imagined a fsgnre being moved, and not the entire plane—even though it was
mentioned many times over that it is the plane that is moved, and not just a figure. This suggests
to me that there is much to be uncovered before a complete characterization of operativity in
transformation geometry can be made.
CONCLUSION
I have taken the position that skilled behavior in mathematical problem solving is a manifestation

of highly structured thinking at a number of levels of thought. With that position in mind, I
outlined a theoretical basis for design principles of mathematics curr icula and offered two
examples of curricula designed accordingly.
The examples of curricula that were designed according to these five principles were drawn from
integers and transformation geometry. Each was structured so that its aim was first to have the
students construct the objects of the subject matter as transformat ions between states, and then
to reconstruct them as objects themselves to be transf ormed. The case of transformation
geometry was the more intricate of the two, as both the states and the transformations are more
complex than is the case with integers
The preservice elementary school teachers in my courses found the curriculum for
transformation geometry to be very difficult. Many found the one for integers to be diff icult as
well.
The case of integers deserves a special comment. It was common at the outset for the students in
my courses to attempt to translate complex INTEGERS expressions into x‟s. ys, + „s, and -„s,
especially when all they wanted was an answer. Apparently they tried to assimilate the questions
into structures they already possessed, as would anyone. However, one must not assume too
much about the nature of those structures. As part of the introductory lecture to integers, I asked
the students why it is reasonable (as opposed to correct) to rewrite —(x — —y) as —x — y.
There was not a single response that sugg ested other than an instrumental understanding
(Skemp, 1978) of signed expressions.

Nor could I elicit a response that referred to quantities. Approximately three weeks after they had
been through the INTEGERS curriculum. I gave them the expression
—(--x ÷ y) x + —y, and asked them why removing the parentheses and changing the signs is a
reasonable thing to do. They resorted, without my encouragement. to an INTEGERS
interpretation, or they said nothing at all. This suggests to me that prior to working with the
INTEGERS microworld they had a weak semantic base, if they had one at all, for the rules by
which they transformed algebraic expressions. This further suggests that those who do develop
mental operations in regard to algebra do so as reflections of transformations of quantities.
The Miseing Link

I hope the reader has not developed the impression that the curricula discussed in the case studies
are teacher-independent. On the contrary, they are actually more depend ent upon the teacher
than are convention.J curricula. Moreover, I can easily imagine that in the hands of some
teachers we would see very little difference, in terms of what students learn, between them and
non-problem-based curricula. All it would take is a teacher whose approach is to demonstrate
“the way‟ to solve problems “like this.‟
Underlying the case studies was an assumption char instruction would be in the hands of teachers
who are thoroughly intimate with the subject matter, and intimate in two ways. Ideally, teachers
should not only possess the cognitive structures that the curr iculum aims for in the students, but
possess them at a reflected level. They should understand the subject matter both intuitively and
formally.
Second, teachers must be—for want of a better word—choreographers. They must have a
structure that they can “dance” through as they confront the obstacles that are ine vitable in the
flow of classroom interactions. To my way of thinking, the only structure that can provide a basis
for such flexibility is a personal model of the genesis of the cognit ive objectives.
Another issue in the case studies was student affect. In my experience, it was not unc ommon, at
the outset of a course, for students to go through an activity, record the information that they
generated, and then say, “1 don‟t understand what the answer is supposed to be.” Many students
never stopped being “answer” oriented, and they became extremely frustrated. If getting tight
answers wasn‟t the name of the game, then they didn‟t know what the game was. They did not
understand that “the answer” was most typically a method, or a generalization of a method, and
not a number. It was ext remely frustrating to me not to be able to influence those students‟
perspective on mathematics.
The Role of Cognitive Science
My concluding remarks are on the role that cognitive science can play as an inspirat ion for
problem-based mathematics curriculum development. Reif (1980) and Larkin (1980) each
commented that the nature of skilled problem solving and cognition is well enough understood
that educators should look to cognitive science for guidance in bow to bring them about. My
assessment, however, is that at this moment the role of cognit ive science in mathematics
curriculum development should be minor and indirect.

I have three reasons for such an assessment. The first is that the models of mathem aucal
problem solving one finds in cognitive science tend to do their jobs all too singlem indedly—and
all too knowledgeably, in the sense that a model knows what it means to solve a problem. I have
yet to see a problem-solving program daydream about an upcomi ng fishing trip while working a
problem, or be distracted by a stray, but related. thought. Nor have I seen a program play a
guessing game with the questioner as to what type of answer, among all the worldly categories it
possesses. the questioner wants (Thompson. 1982b). Does the questioner want an answer, an
historical account of the answer, or an explanation of why an answer has to be correct? The
decision is usually made by the programmer.
The second reason is that, as far as I can tell, little attention has been given to the issue of the
development of mathematical objects in people‟s thinking. Numbers become things to most
children, while for quite awhile they were not; operations become things to some high school
students; functions, groups, classes, categories, and functors become things to mathematicians.
Until cognitive science deals with the nature and development of mathematical objects, I see
little that it can offer as guidance for developing problem-based mathematics curricula.
The third, and most important reason for believing that cognitive science is of limited help in
developing mathematics curricula is that most models of mathematical cognition fail to take into
account the conceptual bases from which cognitions arise. For example. Silver (in press) found
that young adults‟ thinking about operations on rational numbers is tremendously influenced by
the specific models of rational numbers that they bring to mind (e.g., pie charts and measuring
cups). Admittedly, mental representations have been of interest in cognitive science for some
time now, but the issue that seems to be left aside is that of a mental re.presentation of an action
upon a representation. As pointed out in the discussion of integers as mathematical objects, a
transformation is not identifiable with the states upon which it acts. It can only be idei*ified with
a class of states, and in fact genetically predetermines that class. In my way of thinking, until the
notion of action is brought into investigations of mathematical cognition, we will get litt le
guidance from cognitive science regarding the promotion of operative thought in a subject matter
area
I do not mean to give the impression that cognitive science is irrelevant to mathe. matics
education. I find the work of Lawler (1981) and diSessa (1982) to be fascinating and very much

in line with the aims I have expressed here, but theirs seems to be a minority view in cognitive
science.
The recent focus in cognitive science on investigations of structures in problem solvi ng has been
highly illuminating about the ways we don‟i want students to understand mathernaucs—for
example, understanding mathematics as consisting largely of collect ions of routine algorithms
and associated stereotypical problems (Hinsley et al., 1977). Also, the computer metaphor of
cognitive science provides a powerful way to think about mathematical cognition. But we should
not reify the central processing unit; we should not forget that the computer metaphor is only a
metaphor (cf. Simon, 1972).
Where, then, can mathematics education find guidance for developing problem‟ based curricula?
I find Piaget‟s genetic epistemology to be most helpful, but only in that it frames the task of
influencing others‟ thinking. It sets design principles for the theory of cognition that will underty
the specifications of the cognitive objectives (recalling that cognitive objectives must include a
developmental side).
The details of a curriculum must come from an interaction between conceptual analyses of the
subject matter (knowledge as held by competent knowers) and investigations of the genesis of
chat knowledge vls-1-vis instruction. That is. mathematics educaa on must look more so itself
than to any other source for guidance in developing probl em-based mathematics curricula.
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APPENDIX: SUBSET OF COMMANDS
AVAILABLE IN MOTIONS
Command Action
CL Cleans the screen; erases all but the current figure.
CLS Clears the screen; places the figure at home position (HDG 90, POS 0 0, and orientation
right).
DEF “name
(l‟irt of commands] Defines “name as the name of (list of commands], where the commands in
the List are among those allowed by MOTIONS. MOTIONS will respond “name DEFINED” if
it accepts the definition.

If the commands in [last of commands] take variable input, then the list must begin with a list of
the variable names. A variable name must be preceded by a colon within the definit ion itself.
The colon means “value of the following name.”
236 P. W. Thompson
Example: DEF TWO.FUPS ((X Y] F :X F :Y] defines a motion naine d TWO.FLIPS that takes
two inputs, and performs two flips. The first flip is performed about the line defined by the first
input; the second flip is performed about the line define d by the second input.
F <degrees> Flips the plane through the line that passes through the origin at an angle of
measure <degrees>
GRP Places the current figure at the position. heading, and orientation last recorded by RP.
ID Identity motion—leaves plane as it is.
R <degrees.> Rotates the plane about the origin through an angle of measure <degrees>
RP Records the current figures position. heading. and orientat ion. (See GRP.)
T<disgance> <beading> Translates the plane <distance> turtle steps in a heading of
<beading>
MOTIONS maintains several variable values to which reference may be made within a
definition. These are:
Variable
:XCOR The current figure‟s x.coordinate.
:YCOR The current figure‟s y-coordinate.
:HDG The current figure‟s heading.
:ANGI.E The measure of the angle formed by the current figure‟s posit ion, the origin, and the
positive x-sxis.
For example. T:XCOR 180 translates the plane so that the current figure has an x-coordinate of
0.

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