Students' contributions that are not yet mathematically complete, precise, or correct are crucial for learning through classroom discussions. We aim to support teacher candidates (TCs) to see students' ideas as evidence of sensemaking and to respond in ways that keep student thinking central to the discussion. Although approximations of practice are a promising pedagogy for supporting TCs' learning, more research is needed to link features of approximations and TCs' opportunities to learn. Using data from a multiyear collaboration across two institutions, we investigate the use of coached rehearsals and how the design feature of "planted errors" contributed to multiple components of teacher learning in part through the impact on key features of approximations of practice. Our findings illustrate the available opportunities for TCs to develop skill with a complex practice. These results offer implications for the design of approximations of practice and approaches to studying their role in teacher development.