Brain power is physical. Just as exercise builds a child’s muscles, bones, heart, and lungs, so it builds the brain, fueling cells with oxygen, nourishing connections between neurons, and supporting new neuron growth. Yet only one in three American children is physically active daily; fewer than one in seven walks or bikes to school; and, according to a new study from Harvard University’s T.H. Chan School of Public Health, over half are on a track that will lead to obesity by the time they are 35. Schools, where kids spend up to half their waking lives, represent a major opportunity to develop children’s brains, and their health overall, by getting them moving.