The school library media program began as an idea to transform school libraries from warehouses of books into centers staffed by professionals that provide a wide range of educational resources. This was the first revolution in the mid-20th century. The second revolution involved teachers and librarians collaborating using the full resources of the library for instruction. The third revolution pushed for libraries to become active participants in classroom instruction. Standards developed in the late 20th century guided the instructional role of the modern school library media program.