In this systematic review, we examined the rigor and outcomes across 27 object play intervention studies using single-case research methodology. We focused on studies including children age 5 years or younger and examined several descriptive characteristics including materials, instructional packages, and settings. We also analyzed the facilitation and measurement of generalized play and several methodological features including quality, rigor, and visual analysis procedures. Overall, the identified studies demonstrated positive outcomes, although quality and rigor limited interpretations of the outcomes. Previous reviews also have noted strong outcomes and weak to moderate quality for single-case studies. Our results should be interpreted with caution given previous reviews of play intervention studies identified strong outcomes and quality from group-design studies. Additional replications testing robust interventions using single-case research with strong methodological rigor are warranted.