This SGER proposal will make it possible to sustain an effort by precollege classroom teachers to investigate diagnosis of students' knowledge and reasoning in physics and mathematics, especially as the results of the diagnoses are used to guide subsequent instruction. The project is an example of a practical interaction between research on teaching and learning. Development of instructional materials and teacher development. The investigators will revise and use an diagnostic teaching system (begun under an earlier private sector grant) to build a knowledge base of student thinking from which interrelationships between thinking in various topic areas within physics and between thinking in physics and in mathematics. The assessment of student thinking will guide revision of instructional materials and activities to make them more relevant to students' initial conceptions and reasoning. Four teachers, including the two PIs, will interact as peer mentors addressing questions relevant instruction. Expected products include a publication on diagnosis of student thinking in physics and mathematics and a paper about collaboration among peer teachers as a framework for developing more reflective practitioners, for developing the teacher as researcher.