Mixing problems increases performance of all students but especially of low-achieving ones in college calculus

College mathematics courses often act as gatekeepers to studies in science, technology, engineering, and mathematics (STEM). Increasing student performance in these courses is highly important to meet STEM workforce demand. We investigated whether interleaved and spaced homework sets, where problems on different topics are mixed across multiple assignments, increase students’ grades on exams compared to traditional blocked homework sets where problems are grouped by topics. Using a quasi-experimental design, students in two sections of a large ( N = 585) undergraduate calculus course completed either interleaved or blocked homework sets. Interleaved homework improved final exam performance for all students while disproportionately benefiting students with a below or slightly-above average initial performance. Our results indicate that interleaving was particularly beneficial for underrepresented minority and first-generation students. A change in homework structure can be a promising way to both help all students improve their performance while also reducing equity gaps in university mathematics courses.