Everyone who has a child in a competitive hobby knows the types: the boy who disputes every call the referee makes, the parent who hurls invective from the sidelines, the girl who can barely bring herself to shake hands after her team loses. Playing sports and games is hugely valuable for child development: They learn teamwork, strategy, patience, and get a workout to boot. But things go awry when kids can’t place winning and losing in the proper perspective—when a loss is devastating or a win is cause for unseemly gloating.

Everyone who has a child in a competitive hobby knows the types: the boy who disputes every call the referee makes, the parent who hurls invective from the sidelines, the girl who can barely bring herself to shake hands after her team loses. Playing sports and games is hugely valuable for child development: They learn teamwork, strategy, patience, and get a workout to boot. But things go awry when kids can’t place winning and losing in the proper perspective—when a loss is devastating or a win is cause for unseemly gloating.