Active-learning pedagogical practices are encouraged in the education literature to improve academic outcomes. The research reported in this paper explored the effect of real-time interactive polling--a type of active learning--on three measures of academic outcome: final marks, student engagement, and failure probability. To provide credible impact estimates, a cluster randomized controlled trial in an introductory statistics class was conducted. With a little over 500 students, nine out of the 24 tutorial classes were conducted with real-time quizzes; the other 15 tutorial classes served as control classes. The results showed that this active-learning technique did not impact final marks and the probability of failing the subject. It did, however, increase tutorial attendance by about 24%, which corresponded to about 1.6 additional hours compared to the control classes. The findings support the literature on the benefits of classroom response systems that increase student engagement, student interest, and enjoyment from smaller group discussions.