And What of Cohort Size?

Smaller is better. At least, it is when it comes to class size. Both academic literature and popular consent agree: The smaller the class, the more time, attention, and resources teachers have to impact their students. Further, “small” signals that barriers associated with scarce resources have been overcome. But what of the influence of the incoming grade’s size? Regardless of any preplanning, students entering a specific grade find themselves more or less equally distributed among available facilities and teachers. How might this factor affect the ability of instructors to maintain effective classrooms and the capability of districts to manage student populations? What outcomes do larger cohorts experience when compared to smaller ones?

A recent paper by Phillip Babcock, Kelly Bedard, and Jennifer Schulte addresses this gap in research by evaluating the issue in terms of grade retention. The team supplements much-cited literature on Project STAR, which ultimately concludes that students in larger classes have lower test scores and are more likely to repeat a grade. By extending popularized “small-scale studies” to cohort size, the researchers draw corresponding conclusions.

Focused primarily on transitions from kindergarten through the early grades, the authors make extensive use of national data on grade-specific enrollment counts which they describe as, “of uncommon breadth and scope.” Additionally, they utilize the experimental advantage that, in focusing on cohort size, other dimensions associated with student retention remain constant. While an exceptional teacher may luck into a small class, chance placement diminishes in influence at the cohort level.

Thus, after controlling for selective migration, the researchers arrive upon impressively robust results with a sample of 14,000 districts by following the number of students held back in primary grades as a result of inclusion in larger cohorts. From this sample, evidence at the national level suggests that a ten percent increase in kindergarten enrollment is associated with shrinkage of 0.5 percent to the grade-level cohort each year. Of students held back, those performing poorly at the onset disproportionately suffer this ill-effect.

Certainly, the possibility remains that schools or districts might use grade-retention as a strategy for evening out swelling cohorts and that underachievement does not necessarily increase. Regardless, the paper’s findings are clear: a smaller school, a smaller classroom, and, now it seems, a smaller cohort all provide advantages. But before policymakers take action on this issue, more research is needed to understand the complimentary costs associated with decreasing school size. Small is good, but it’s also expensive.

Feature photo: cc/Ol.v!er