You also have to consider that women are sometimes bullied into breastfeeding even when it's very hard for them and that is the author's main message. Otherwise she still thinks that "breast is best": "Breastfeeding seems to improve digestion in the first year, lowers rashes for infants and is especially important for preterm babies. It also seems likely that it has some impact on reducing ear infections in young children and lowers the risk of breast cancer for the mother."

"Breastfeeding in the 21st century: epidemiology, mechanisms, and lifelong effect" - https://www.thelancet.com/journals/lancet/article/PIIS0140-6...

* it's study not studies

* it refers strictly to educational performance

* it's likely detecting something else entirely: "The researchers found that same-sex parents are often wealthier, older and more educated than the typical different-sex couple. Same-sex couples often have to use expensive fertility treatments to have a child, meaning they are very motivated to become parents and tend to have a high level of wealth. This is likely to be a key reason their children perform well in school, the economists found" [...] "When the economists controlled for income and wealth, there were a much smaller gap between the test scores of children of same-sex parents and children different-sex parents, although children of homosexual couples still had slightly higher scores."