Evidence-based medicine is often seen as a model for evidence-based education, and deservedly so, but evaluators in education have been slow to adopt one of its salient features, attention to side effects. Many education evaluations focus almost exclusively on efficacy, that is on achievement test scores. Regardless of domain, all interventions produce collateral effects beyond those sought by the interveners. As people continue to learn in medicine, in agriculture, and in warfare, failure to consider collateral effects may and often does lead to ill-advised recommendations. Acknowledging that educational interventions produce side effects raises two key questions for those seeking to incorporate them in evaluations: (1) Which side effects?; and (2) How can they be assessed? The problem in education is not the absence of collateral learning but its abundance. Evaluators ought to be obliged to assess the collateral learning which suffices to call into question a verdict based on measures achievement measures alone. One kind of collateral learning "unequivocally" meets this requirement, namely motivation to continue learning (hereafter, CM). A reduction in CM need not always outweigh a gain in academic achievement. However, "evidence concerning the strengthening or weakening of CM is always relevant to, and may overturn a verdict based solely on achievement measures." The author does not deny that educational experiences strengthen or weaken other important dispositions and the more of them that evaluators can incorporate, the better, but assessing CM ought not to be optional.