The authors contend that children benefit from play as a form of intervention and as a means of fostering their cognitive, social, and physical growth. They review several standardized instruments developed over the last fifty years to assess this benefit of play on child development. They identify twenty-one such play measures, the majority of them applicable to children under twelve. Some of the measurements can be conducted by children, but most are proxy rated and employ some form of observation. Over half require no or minimal training. Others can be completed in less than thirty minutes. More evaluations exist for the earlier instruments, but these measurements lacked psychometric evidence to back them up. The authors note they based their selections on the distinct characteristics and features of the measures, and they offer their conclusions to assist users in choosing the best systematic instruments for their specific needs.