Background Undergraduate teaching assistants (UTAs) are associated with increased student performance and belongingness. Yet, when given a choice, not all students leverage UTA-facilitated opportunities equally. Objective This study explores motivational and contextual factors that underlie individual differences in students’ willingness to attend UTA facilitated supplemental workshops and the impact of such engagement on their achievement. Method Undergraduates ( N = 112) in research and statistics courses completed measures of help-seeking, social fit, and expectancy value three times across the semester. Responses were compared to students’ attendance records, exam scores, and open-ended responses evaluating benefits and challenges of working with UTAs. Results Given the choice, a majority of students chose to attend workshops and consistent participation was positively correlated with exam performance. Yet help-seeking intentions, social fit, value beliefs, and perceived obstacles rather than incentives or perceived costs explained individual differences in workshop participation itself. Conclusion UTAs can improve peer’s achievement but simply providing students with opportunities to interact with UTAs is inadequate. Scaffolding active participation in UTA-led workshops requires addressing students’ motivational orientations. Teaching Implications To improve participation in peer-led opportunities, UTAs and faculty must generate an integrated model emphasizing value, normalizing help-seeking, and working to remove barriers.