This chapter begins by highlighting the findings of recent narrative reviews on outcomes of instructed heritage language acquisition. Further, it describes the advantages of quantitative meta-analysis, which has proven to be an effective research synthesis method to identify patterns in study findings and to determine under-investigated variables. The bulk of the chapter is devoted to a description of an exploratory quantitative meta-analysis of the research on instructed heritage language acquisition to date. The grand weighted effect size for the over-arching question, “What impact does heritage language instruction have on heritage language ability?” was d =.57, indicating that heritage language instruction has a moderate, positive effect on heritage language development. The need for more detailed reporting, echoing similar calls in second language acquisition, is emphasized; attention to variables identified by the meta-analysis as under-studied are drawn; and a call is made to conduct longitudinal studies in order to trace the impact of instruction beyond the short term. The conclusion stresses recommendations for multi-site research and replication, a strategy that will help to move the field forward, especially in heritage languages with smaller populations of speakers or speaker populations that are geographically dispersed.