Smaller Class Sizes May Disproportionately Benefit the Strongest Students

Mandating smaller class sizes is a popular idea for raising academic achievement, and some of the most well-known support for the it comes from the STAR program — an initiative in Tennessee in the late 1980s in which over 11,000 K-3 students were randomly assigned to small classes (13-17 students), regular classes (22-25), or regular classes with a full-time teacher’s aide. Although past evaluations of STAR have found that the smaller classes significantly raised achievement for low achievers, a new analysis of the program is now calling the implication of those findings into question.

Two UC Davis researchers, sociologist Erika Jackson and economist Marianne Page, claim that previous research on STAR doesn’t tell the whole story because it tends to focus on average gains. They decided to look at the distribution of gains, and they found that even though at-risk students posted larger gains in smaller classrooms on average, a greater share of those gains went to the at-risk students who were the highest achievers. In other words, the small classrooms were more likely to help the best of the worst.

Jackson and Page explain:

For example, the test score of a student at the 90th percentile in a small class is a little less than a third of a standard deviation higher than the test score of a 90th percentile student in a regular class, whereas test score differences at the 10th percentile of the distribution are less than a tenth of a standard deviation.


Our estimates are consistent with Nye et. al.’s finding that low-achievers do not benefit more than high achievers, but is even stronger, as we find that the gains to small-classes actually increase with achievement. Our confidence intervals are generous, but the pattern is notable, and appears to contrast with sub- group analyses of class-size effects, which suggest that it is students who are most “at-risk” who benefit most from smaller classes.


A common inference is that class-size reduction policies are most beneficial to at-risk populations. Our analyses suggest that if populations at-risk are determined according to test score achievement, then the reverse may actually be true: the biggest gains from the experiment were at the top of the achievement distribution. This pattern is evident both within and across subgroups, but the gains at nearly every quantile are larger for blacks than for whites, which is why the average test score gain for blacks exceeds that of whites even though blacks are more concentrated at the low end of the achievement distribution.

One thing that’s interesting is that there tends to be a lot of overlap between opponents of charter schools and proponents of smaller class sizes. However, according to Jackson and Page one of the more legitimate criticisms of charter schools — that they benefit the higher achievers among the lower achievers — also applies to smaller class sizes.

When you think about it, these findings aren’t all that surprising. High-achievers are those who excel in a standard classroom environment, and smaller classes enhance that environment rather than alter it. I’ve touched on this before, but simple Bayesian reasoning suggests that it’s the students who struggle in a given classroom who will benefit the most when the structure of the classroom is altered. In fact, evaluations of cognitive tutors and interventions that make heavy use of technology often show the largest gains for the weakest students.

In the end this is merely one set of data on 11,000 kids who went to school in Tennessee in the late 1980’s, but if future research confirms this “best of the worst” effect it would be a big boost to the idea that helping the most at-risk students requires radical changes to the standard classroom. That could mean flipping it, filling it with cognitive tutors, or following some other design that’s currently hiding away in a small district or university lab.
Jackson, E., & Page, M.E. (2012). Estimating the Distributional Effects of Education Reforms: A Look at Project STAR Economics of Education Review DOI: 10.1016/j.econedurev.2012.07.017


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2 Responses to Smaller Class Sizes May Disproportionately Benefit the Strongest Students

  1. James says:

    Very interesting. The failure of California’s massive class size reduction experiment is usually blamed on the relaxation of credentialing that it necessitated, which leaves the argument for class size reduction in place, at least theoretically–it was just an implementation problem. But this study suggests that class size reduction may be fundamentally flawed as an approach to raising scores of low scoring students.

  2. Pingback: Remainders: Tracking the 300,000 teacher job loss gap | GothamSchools

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