There are, of course, some benefits to attending a competitive high school. The study found that students at selective schools were less likely to be suspended or to miss school and reported that they felt safer. In addition, students who attended high-scoring non-selective schools did see academically significant benefits relative to those at low-achieving schools.

The study highlights the challenge of measuring school quality and suggests that many parents and education policymakers are judging schools by the wrong metrics.

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The study, conducted by four researchers affiliated with the consortium, was published this month in the peer-reviewed journal Educational Evaluation and Policy Analysis. The researchers examined ninth-graders who entered Chicago’s public high schools, including charter schools, between 2008 and 2011. Interestingly, about two thirds did not attend their zoned neighborhood high school in the 2011–12 school year.

The researchers divided schools into four groups: selective, top-tier, middle-tier, and bottom-tier. The first group consisted of schools that admit students based largely on test scores. The latter three groups were ranked by their students’ ACT scores and high-school graduation rates.

The study compared students against peers who attended different-tier schools but were otherwise similar based on traits including past test scores, degree of parental involvement, and home neighborhood. This approach isn’t perfect, but it allows researchers to estimate the impact of schools while holding student characteristics constant.

When simply making raw comparisons between students at selective-enrollment versus other city schools, the differences appear stark: Students at selective schools scored more than seven points higher on the ACT, which has a maximum score of 36. Yet when researchers controlled for a variety of factors to isolate the effect of attending a selective school, the disparities all but vanished. Attending a selective-enrollment school led to only a statistically insignificant bump in the ACT of half a point. The selective schools also seemed to have little or no effect on the likelihood of taking Advanced Placement classes, graduating from high school, or enrolling and staying in college.

Selective schools did, however, produce a variety of non-academic gains: Students had higher attendance and lower suspension rates, and they trusted their teachers more. Students also reported that their peers’ behavior was much better and that they felt safer in school—this suggests that insofar as selective schools are beneficial, it may be because of higher-achieving peers rather than better-quality instruction.

Again, to get these results, the study compared students at selective schools with similar students at different schools. Notably, though, the second group of students largely ended up at relatively high-achieving schools in the city—very few went to Chicago’s lowest-scoring schools. And so, the lack of academic boost students gained from the selective schools may be attributable to the relative quality of the fallback schools in comparison.