The two research projects described and discussed in the special issue provided much needed longitudinal empirical data to show the curricular influence on classroom instruction and student learning outcomes. The findings have helped to advance our understanding of whether the reform curricula can bring about positive changes in classroom instruction and student learning outcomes and how such changes might be sustained. In this article we synthesize the results from the two studies and discuss several lessons learned from the projects about investigating and understanding curricular effects on the teaching and learning of mathematics.