Multitiered systems of support provide a framework for matching the needs of a struggling student with an appropriate intervention. Experimental evaluations of tiered support systems in grade schools have been conducted for decades but have been less frequently examined in early childhood contexts. A recent meta-analysis of multitiered systems of support in preschool settings exclusively synthesized outcomes from group design studies. Our current review extends this review by synthesizing single-case research examining interventions implemented within tiered support system frameworks in preschool settings. Our data indicate that single-case evaluations of tiered support systems do not frequently meet contemporary standards for rigor or consistently identify functional relations. Recommendations and considerations for future research are discussed. (author abstract)