Given the scarcity of scaffolding in classrooms, we developed a professional development program (PDP) focusing on scaffolding. The PDP was based on a model of contingent teaching consisting of three steps: diagnostic strategies, checking the diagnosis and intervention strategies. The development of four social studies teachers' scaffolding knowledge, use of scaffolding in practice and reflections on practice were analyzed. Insights regarding openness, students' understanding, and co-construction--that occurred while reflecting with the model of contingent teaching--appeared to foster teachers' scaffolding development. A fourth step, checking students' learning, is suggested as an additional step in contingent teaching. (Contains 1 table and 6 figures.)