The authors examined the effects of team-based learning (TBL) implemented in Grade 8 social studies classes on student content acquisition. Twenty-four classes were randomly assigned to treatment or comparison blocking on teacher. In the treatment classes teachers integrated TBL practices in the content instruction. The authors examined teacher instruction in the treatment and comparison classes during implementation. Results indicated TBL was implemented only in treatment classes and teachers demonstrated a novice level of implementation. The authors then examined the effects of the treatment implementation on measures of content acquisition. Significant differences in favor of the treatment condition were noted in the number of accurate content ideas produced in a written essay (effect size = 0.31). A small effect (0.16) was also observed in the number of supporting details students provided in the essay but was not statistically significant. There was no benefit of the treatment on a multiple-choice test of content knowledge.