The school was built for a capacity of 2,500 students, and when it opened in 1923 it had about 500 students. Due to an enrollment decline in the 1950s the Los Angeles City High School District considered closing Belmont. By the 1990s the school had its peak enrollment, 5,500 students, making it California's largest high school and one of the largest in the United States. During that period many students were reassigned to and sent on buses to schools in the San Fernando Valley because there were too many students in Belmont. In the 1997-1998 school year the school had 5,160 students. At the time, the school's dropout rate was 65% and in terms of its four-year graduation rate it ranked lower than 96% of Los Angeles County high schools. 72% of the enrolled students took free lunches.