This is just an observational study. It seems fairly useless for understanding whether a given person will be smarter if they learn a second language. Looks li

This is just an observational study. It seems fairly useless for understanding whether a given person will be smarter if they learn a second language. Looks like the “controlled for” socioeconomic status, but I doubt this fully captures the difference in populations between bilingual and non-bilingual people. It could be that the population of bilingual people, had they not been bilingual, might have scored lower on these tests, and therefore being bilingual brought them up to par. Impossible to tell.