Children have been found to learn less in school when there are more boys in the classroom. We make two contributions to the literature. First, we revisit the empirical approach based on within-school grade-level variation. We find that with grade retention (a feature of most school systems) the approach is subject to a selection bias that generates effects of boys on their classmates' skills in the absence of any peer effects. We propose an alternative based on variation across enrollment

Tag-uri: Italia