University class structure is changing. To accommodate working students, programmes are increasing their offerings of long night classes – some lasting as long as six hours. While these long classes may be more convenient for students, they have unintended consequences as a result of cognitive load. Using a panel of 124 students (372 observations) and a differencing approach that controls for student characteristics, we show that student exam performance decreases by approximately one-half letter grade on content taught in the second half of a long class (significant at the 5% level).