Behavior analysis differs from most psychological accounts of human development. Under developmental stage theories, what children are ‘likely to do’ at ‘approximately what developmental level or age’ are emphasized, but not ‘how or why they do it—the process—is undisclosed and largely unknown. Those who focus on the development of hypothetical structures often miss many of the observable behavioral phenomena that are of importance in development. Pseudo-explanations like stage and critical periods do not lead to better prediction or control of the behaviors or mental capacities being studied. Further, such theories often invoke internal processes as causal factors, advancing hypotheses difficult to confirm/disprove with empirical research. Behavioral-analytic theory conceives development to be progressive behavior changes shaped by consequences. These behaviors in turn become “hierarchically organized.’ Behavior analysis is both a methodology for studying human development and a proven technology for increasing intellectual abilities and teaching useful skills. In this chapter we attempt to show that planned interventions based on this empirical behavioral foundation should be more effective and have more durable outcomes.