In this multicountry analysis, we generate a student-level measure of socioeconomic
status (SES) “mixing” to understand the benefits or pitfalls of placing
low-SES children with diverse peers. We conduct this analysis separately for
equal and unequal countries that provide the same curriculum to all children
regardless of ability level, and we find some surprising similarities. For example,
lower mathematics and science test scores are associated with low-SES children
in mixed classrooms. We then apply this analysis to the United States, a rich
but unequal country where ability-based tracking is common. For the United
States, we find that the cross-national patterns are reversed for mathematics,
and socioeconomic mixing is beneficial for low-SES children; however, the results
for science are not significant.