The purpose of this review was to quantitatively synthesize studies on functional communication training (FCT) for young children exhibiting challenging behavior when FCT was delivered in early care and education settings. Twenty studies published in peer-reviewed journals between 1992 and 2016 that met established inclusion criteria were reviewed and coded on variables associated with child-level, interventionlevel, and study-level characteristics. The What Works Clearinghouse (WWC) standards for evaluating single-case design research were then applied to each study. Study effects were calculated using the percentage of non-overlapping data and Tau-U. Results indicated that FCT interventions had strong effects for reducing challenging behavior. Findings suggest additional studies with more children and methodological rigor are needed before FCT can be characterized as an evidence-based practice for the treatment of challenging behavior of young children with disabilities in early care and education settings based on the WWC's evidence-based criteria. Limitations of the present synthesis and implications for future research are discussed.