Teachers' ways of using curriculum materials create not only meaningful learning opportunities for students but also opportunities for teachers to learn and change their teaching practices; however, not enough research has investigated precisely how. This study investigates how teachers' implementation of innovative curriculum materials specifically designed to support formative assessment practices provides learning opportunities for teachers to become more responsive to student mathematical thinking. 2 teachers' regular lessons as well as those delivered using the innovative curriculum materials were observed; each teacher was observed over the course of 1 academic year. The analysis of the 2 teachers' cases demonstrates how their different curriculum adaptation strategies led to different learning opportunities for each of them. Although teachers' enactment of innovative curriculum materials in class naturally creates opportunities for them to learn about the mathematical content as well as their students' mathematical thinking, these findings discuss precisely how to promote teacher learning and improvement of teaching practices using formative assessment strategies guided by curriculum materials. The implications in relation to supporting teachers' instructional improvement while implementing reform-oriented curriculum materials, and to designing curriculum materials facilitating teacher learning, are also discussed.