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The authors use nationally representative survey data and a research design that relies on contemporaneous within-student and within-teacher comparisons across two academic subjects to estimate how class size affects certain non-cognitive skills in middle school. Their results indicate that smaller eighth-grade classes are associated with improvements in several measures of school engagement, with effect sizes ranging from .05 to .09 and smaller effects persisting 2 years later. Patterns of selection on observed traits and falsification exercises suggest that these results accurately identify (or possibly understate) the causal effects of smaller classes. Given the estimated earnings impact of these non-cognitive skills, the implied internal rate of return from an eighth-grade class-size reduction is 4.6% overall, but 7.9% in urban schools.

To investigate the impact schools have on both academic performance and cognitive skills, the researchers related standardized achievement-test scores to measures of cognitive skills in a large sample of eighth-grade students attending traditional, exam, and charter public schools. Test scores and gains in test scores over time correlated with measures of cognitive skills. Despite wide variation in test scores across schools, differences in cognitive skills across schools were negligible after we controlled for fourth-grade test scores. Random offers of enrollment to oversubscribed charter schools resulted in positive impacts of such school attendance on math achievement but had no impact on cognitive skills. These findings suggest that schools that improve standardized achievement-test scores do so primarily through channels other than improving cognitive skills.

We used self-report surveys to gather information on a broad set of non-cognitive skills from 1,368 8th-grade students attending Boston public schools and linked this information to administrative data on their demographics and test scores. At the student level, scales measuring conscientiousness, self-control, grit, and growth mindset are positively correlated with attendance, behavior, and test-score gains between 4th- and 8th-grade. Our results therefore highlight the importance of improved measurement of non-cognitive skills in order to capitalize on their promise as a tool to inform education practice and policy.