The Common Core State Standards for Mathematics (CCSS-M) aim to engage students in complex mathematical practices, including modeling, reasoning, and argumentation. Currently, little is known about how teachers' daily instruction supports these practices. This study draws upon data from daily logs completed by third-, fourth-, and fifth-grade mathematics teachers from 39 states to learn about students' engagement in standards-aligned mathematical practices. We find that there are both substantial fluctuations in students' engagement in these practices and reported cognitive demand from day to day, as well as large differences across teachers. Practices in which students engage are related to teachers' perceptions of student ability. These findings offer a broad perspective on how CCSS-M--based instruction unfolds across a range of states and policy environments.