ManyClasses 1: Assessing the generalizable effect of immediate versus delayed feedback across many college classes

Psychology researchers have long attempted to identify educational practices that improve student learning. However, experimental research on these practices is often conducted in laboratory contexts or in a single course, threatening the external validity of the results. In this paper, we establish an experimental paradigm for evaluating the benefits of recommended practices across a variety of authentic educational contexts – a model we call ManyClasses. The core feature is that researchers examine the same research question and measure the same experimental effect across many classes spanning a range of topics, institutions, teacher implementations, and student populations. We report the first ManyClasses study, which examined how the timing of feedback on class assignments, either immediate or delayed by a few days, affected subsequent performance on class assessments. Across 38 classes, the overall estimate for the effect of feedback timing was 0.002 (95% HDI -0.05 to 0.05), indicating that there was no effect of immediate versus delayed feedback on student learning that generalizes across classes. Further, there were no credibly non-zero effects for 40 pre-registered moderators related to class-level and student-level characteristics. Yet, our results provide hints that in certain kinds of classes, which were under-sampled in the current study, there may be modest advantages for delayed feedback. More broadly, these findings provide insights regarding the feasibility of conducting within-class randomized experiments across a range of naturally occurring learning environments.