This experiment examines the causal effect an electronic classroom response system (ECRS) has on students. Previous studies using an ECRS in the classroom indicate improved performance; however, many have confounds typical of classroom studies. To complement these studies, we conducted a laboratory study to minimize these confounds and concentrate on student engagement. We randomly assigned participants (n = 52) to receive a 10-minute lecture either with or without an ECRS. The lecture contained questions to increase student engagement but not provide student and instructor feedback of concept mastery. Afterwards, the lecture participants were given a surprise quiz. Students using the ECRS scored significantly higher. We discuss the implications of this experiment for the ECRS literature.