People usually live up to their expectations. The kid picked first for dodgeball feels a duty to be the best, and to perform the best, and to be better than anyone else. They feel a need to execute. And, the only way they are going to achieve that is to make their body run faster, jump higher, and move quicker. If more fat kids were chosen first for activities and sports and group/team dynamics, they would automatically start to change their lives to fit into the expectations that surround those moments. Any time a child is picked last, they know it’s because people expect the least of them, and so they never actually have a need to rise above that.