The review includes both correlational and experimental studies examining the effects of play for children ages 3 to 18, examining a range of socio-emotional outcomes. We are especially interested in evidence of causal or long-lasting effects, but such studies are nearly nonexistent. Most existing research focuses on immediate changes during or just after play sessions. Given this scarcity, we’ve also included relevant experimental studies with nonhuman subjects when they provide clear insight into the mechanisms underlying play’s impact on relevant socio-emotional outcomes. (View Highlight)