Examines how science teachers' (n=14) knowledge of science and science pedagogy changed after participation in a constructivist-based methods course. More-experienced teachers were paired with less-experienced teachers, and pre- and post-instructional concept maps, journals, portfolios, and transcripts revealed that, within the zone of proximal development, peers, teachers' students, instructors, readings, and tools mediated knowledge development. Contains 18 references. (Author/WRM)