Milk this for all it’s worth. While there’s strong consensus among medical experts that “breast is best” for babies , the ideal duration of breastfeeding — six months? A year? Until the kid is way too old and it becomes a little creepy? — has always been murkier. New research out of China might offer better-informed advice for when to wean. Analyzing data collected for a national family survey, the researchers found that longer breastfeeding periods gave children a leg up at school, especially