This article introduces an alternative impact parameter for group-based RCTs with student mobility--the survivor average causal effect ("SACE")--that pertains to the subpopulation of original cohort students who would remain in their baseline study schools in either the treatment or control condition. The "SACE" parameter has a clear interpretation, because it pertains to students who would receive maximum exposure to the intervention in the treatment condition, and who would receive a common array of intervention services within each treatment school. For many education RCTs, intervention exposure will be strongly correlated with intervention dosage, and thus, the "SACE" parameter is likely to be highly relevant for "dosage" analyses. Consequently, the methods presented in this article can be used to address the following research question that is often of interest to education policymakers and evaluators: What are intervention effects for the subgroup of students who receive full exposure (or the full dose) of intervention services? This research question is germane to the SREE conference theme, because the "SACE" parameter provides policy-relevant information on the heterogeneity of treatment effects for the subgroup of the full study population who remain in the study schools throughout the follow-up period. Clearly, levels of intervention dosage cannot always be mandated. However, understanding program effects for those who are exposed to intervention services for the full follow-up period provides policy-relevant information on likely program effects that would be observed if intervention implementation was improved or became more widespread. Thus, the estimation of the "SACE" parameter can strengthen overall RCT findings.