Theories regarding the long-term effects of educational interventions are often assumed, but rarely tested using experimental methods. In the following commentary, we argue that the shortage of randomized control trials with long-term follow-up presents serious problems for the field, as it hampers our ability to develop educational programs that produce long-lasting effects, and creates incentives for the research community to focus too much attention on short-run impacts. We present steps that both researchers and funders could take to substantially improve the educational research literature by investing in educational experiments with long-term follow-up. [This paper was published in "Journal of Research on Educational Evaluation."]