Because children spend so much of their time in schools, their playgrounds offer a good setting for promoting active play in young lives. Teachers, instead of considering active play a taxing demand on their busy day, have begun to develop an informal curriculum for it. The authors review the research on children's active play and explores its influence on school playgrounds, looking at studies of individual and social play, the effect of physical environments on active play, and the impact of school polices on children's active play on school playgrounds. They ask others to consider the implications of this research when planning children's active play.