Enrollment at SMJC grew rapidly from the initial class of 30 in 1922: 137 students enrolled in 1923, and the freshman class alone was 102 in 1924. SMJC reached enrollments of 430 students (250 freshmen) in 1926 and 480 students in 1927, when classes moved back to the Baldwin campus. It was the only junior college on the Peninsula until 1935 and attracted commuter students from San Francisco (who used San Francisco and San Mateo Electric Railway and/or Peninsula Commute trains), San Jose, and the East Bay. By 1935, enrollment had reached 1,500, but fell back to 1,000 when San Francisco Junior College opened that fall.
The first classes for workers to develop additional skills were offered in 1932, when a vocational class in aeronautics started. An Adult Program was introduced in 1936 for evening classes at the Baldwin campus, and 500 students signed up by the end of the first week. By 1943, 5,073 were enrolled in evening classes. During World War II, enrollment dropped as many potential students were serving in the military instead; SMJC shifted to teaching servicemen and radar courses. Unused land at Delaware was planted with crops as a victory garden. The college set up a Community Canning Center in June 1944 and had produced 108,000 cans by the end of the year. Enrollment rebounded after the war; although there were only 35 graduates in 1945, there were 1,800 students enrolled in 1946 and 2,400 in 1947, with 307 graduating in 1949. 5,621 attended classes on September 30, 1963, the first day of classes at the new College Heights campus.