This study investigated secondary mathematics teachers' teaching practice. The subjects were enrolled in a three-hour graduate mathematics education course and an accompanying one-hour, school-based PLC for secondary mathematics and science teachers. The goal of the course was to deepenteachers' understanding of rate-of-change and function through a covariational approach to teaching the concept of function (Carlson, Jacobs, Coe, Larsen, Hsu, 2002). The goal of the learning communities was to promote teachers' reflection on the effect of their practice on student learning and to assist teachers in learning to develop conceptually based and inquiry focused lessons.