Breast-feeding longer can make children smarter. That's the conclusion of a study published Monday in JAMA Pediatrics, a journal of the American Medical Association.

In many ways, the study won't surprise proponents of breast-feeding, who have long posited a connection between nursing and cognition and now have an additional piece of research to back up their argument. Skeptics could likely stick to the view that what matters most is how smart a baby's mom is, or that social pressure to breast-feed can have its own problems...