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, which threatens the external validity of the results. In this article, 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, in which we 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% highest density interval = [−0.05, 0.05]), which indicates that there was no effect of immediate feedback compared with delayed feedback on student learning that generalizes across classes. Furthermore, there were no credibly nonzero effects for 40 preregistered moderators related to class-level and student-level characteristics. Yet our results provide hints that in certain kinds of classes, which were undersampled 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.

Vesicular horizons are thin (usually <10 cm) surface or near‐surface horizons characterized by the predominance of vesicular porosity. They are widespread in arid and semiarid lands, occurring on every continent and covering 156,000 km2 of the western United States. Vesicular horizons have critical implications for management due to their role in controlling surface hydrology and dust mobilization. This study evaluates the distribution and variation in expression of vesicular horizons across the western United States using the soil databases available from the USDA. A vesicular horizon index (VHI) that incorporates vesicular horizon thickness and the size and quantity of vesicular pores was developed using soil descriptions from a published chronosequence study. The VHI was applied to descriptions from the soil survey databases to evaluate vesicular horizon expression across the western United States. Vesicular horizons were better expressed (higher VHI) in the Central and Northern Basin and Range compared to the Mojave and Sonoran Basin and Range. This may be due to differences in temperature regime or to larger areas of playas in the Central and Northern Basin and Range that serve as sources of dust that forms the parent material for vesicular horizons. The median VHI was highest in the Aridisols and Mollisols compared to other soil orders. No significant relationship was found between VHI and soil textures. Vesicular horizons are widely distributed in western United States and occur across a wide range of soil types and soil‐forming environments.

CORE IDEAS (85 characters max)• Remote soil judging contests are a viable alternative to in-person contests.• Students gain more mastery of soil science concepts with hands-on practice.• Soil judging participation results in more favorable attitudes toward soil science.• Soil judging, regardless of contest format, is a precursor to a soil science career.

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 class, 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 XX classes, [summarize effect of feedback timing, including key moderators]. More broadly, these findings provide evidence regarding the feasibility of conducting within-class randomized experiments across a range of naturally occurring learning environments.

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