Non-cognitive skills (NCS) contribute to variation in how students respond to challenges inside the classroom and beyond. Competitive policy debate is a co-curricular activity that both encourages cooperative learning and is hypothesized to promote NCS. The goal of this pilot was to examine the relationship between debate participation and change in four NCS among high school students over the course of an academic year. Two surveys (Fall and Spring) were administered during the 2017/18 academic year to students who participated in the Chicago Debate League (n=102). Surveys assessed demographic factors, characteristics of debate participation, and four indicators of NCS each measured using established scales: Growth mindset, grit, mood, and civic engagement. Paired t-tests were used to quantify change in NCS over time. Linear regression was used to assess the relationship between characteristics of debate participation and change in NCS. In the Fall, median length of debate participation was 6.2 months. Average age was 16, most (82%) participants were non-White and 52% were female. Over the academic year, growth mindset increased (Δ=0.29 (95% Confidence Interval (CI): 0.10, 0.48) while grit declined (Δ= -0.17, 95% CI: -0.34, -0.01). Civic engagement and mood were unchanged. Duration of participation was associated with increased change in grit (β=0.04, p≤0.01), but was unrelated to the other NCS. Motivation for joining debate did not explain variation in any NCS. Debate participation is associated with improvement in some NCS. Findings have implications for scalable interventions to promote NCS in the context of cooperative learning.