The aim of this systematic review is to provide insight into the conceptual and methodological credibility of experimental research designs on the effectiveness of team teaching--a promising instructional strategy wherein two or more professionals collaboratively provide education for a group of students. A total of 31 studies were included. These studies were conceptually and methodologically examined according to two actualized quality-appraisal frameworks. The findings reveal that it remains a challenge to design rigorous experimental studies with clear conceptualizations of key variables related to team teaching. To make convincing claims on the effectiveness of team teaching, there is an urgent need for better-defined quality experimental research. Therefore, we conclude with recommendations for future research, specifically how experimental studies on the effectiveness of team teaching should be conceptually and methodologically implemented to provide policymakers and stakeholders with information for evidence-informed decision-making on educational practices.