They usually breastfeed in 3rd world countries. Who is that working out for them?
It’s probably making their children healthier and more intelligent than they would otherwise be, especially considering the sanitation issues with other sources of infant nutrition.
Brazil, where this study was done, is a third world country. If the studied population came from the same socioeconomic class, there might actually be some biological causation going on. On the other hand, extended breastfeeding could be an indicator of other factors - such as a stay-at-home mother who is willing to make a lot of effort for the child - that correlate with greater educational success.
Exactly, if this study were true, then Africa would be full of geniuses ...