The document summarizes research conducted on assessing student performance in geological observation. The research aimed to develop ways to assess students' perception, explanation, and gestures involved in geological observation. Data was collected from video recordings of students in classroom and field activities. Analysis of the data identified components of perception, types of explanations, and gestures used by students at different levels of performance. The research led to a model for assessing geological observation that accounts for conceptual and cognitive development in geosciences.