This study evaluated the impact that trained and supported undergraduate teaching assistants (UTAs) may have had on the academic achievement of students in the first semester of an introductory chemistry course for science and engineering majors. Framed by the concepts of Lave and Wenger's Community of Practice and Wheeler, Martin and Suls' Proxy Model of Social Comparison , the study used an untreated control group with dependent post-test only design. Covariates related to student academic achievement and contextual variables were also collected and used to build models for the final exam core outcome variable. Hierarchical linear models indicated that having a UTA gave students with above-average college GPA a statistically significant boost on final exam score. More importantly, having a UTA was associated with persistence into the next course in the two-semester introductory chemistry sequence, regardless of academic achievement.