First-year (100-level) and second-year (200-level) courses typically have 150-200 students. The lectures for these courses are taught by professors and are complemented by recitations and/or laboratories, taught by teaching assistants to smaller groups of about 30 students. Upper-division (300-level and 400-level) class size ranges from 20-30 students for special topics courses to 60-90 students in the most popular courses.