ManyClasses is a large-scale collaborative research project investigating the generalizability of educational practices in real classrooms. For decades, researchers from psychology, cognitive science, and education have attempted to identify educational practices that improve student learning. When studied in real classrooms, research on these practices is often limited to a single class or topic, which limits the generalizability of the inferences that can be drawn. To better investigate generalizability, a ManyClasses study examines the same research question in dozens of contexts spanning a range of courses, institutions, topics, and student populations. For more information, visit the ManyClasses website.