- An increase of the average socioeconomic status of a student’s peer group with one student-level standard deviation leads to an increase of her test score with 0.32 SD.
- The effect for a “ideal’ study, is 0.315.
- Large differences in effect estimates reported in different studies can to a considerable extent be explained by differences between those studies in their operationalization of peer SES and in their estimation strategies.
- Results show that measures that only used information on parental education lead to much smaller effect sizes (-0.16). In contrast, composite measures and measures solely consisting of parental occupation are associated with about the same effect size.
- Three main characteristics of samples used did not seem to be related to the differences between studies in their reported effect sizes. Peer SES has about an equally sized effect on students’ language, math and science test scores. Peer effects did also not differ between children of different ages. And, in countries that differ in their extent of social inequality, the peer effect does not vary.
- Not including a prior attainment covariate leads to considerably higher effect estimates.
- Found that studies from the field of Social Sciences, ceteris paribus, found smaller effects than studies from the field of Economics.
- SES of a student’s classmates has a substantial effect on her test scores and that obtaining unbiased estimates of this effect, taking into account the pitfalls is worth pursuing.