Bailey argues that the role of causally informative evaluations of interventions within developmental psychology should be elevated. Causally informative research on the effects of intervention inputs on medium- and long-term outcomes are sufficiently relevant to developmental psychology to inform or even constrain our theories and to inspire future developmental research. Bailey reviews examples of research that yielded developmental insights from such work and discusses a broad theoretical framework for using developmental theory to reason about the effects of interventions and vice versa.