Wikipedia says the school opened in 1924, so my guess is the first school year ended in 1925 (according to the year on the school's seal, at left).
Today the building houses a number of small, specialized public schools, but it was originally one huge high school, drawing from many Bronx neighborhoods. It awarded academic diplomas, general diplomas, practical arts diplomas, and commercial diplomas.
Mom and Auntie graduated in January, 1936 (see bottom, where their names are listed in the graduation program she saved). They were just 16. Mom immediately looked for work. Her older brother Fred had gone to college (one of the free City University of NY colleges) but there was only enough money for one more to go to college, so Auntie went (to another free City University of NY college) and Mom didn't. Both Fred and Dorothy went on to earn a doctorate degree.
Mom, who could have done the course work in her teens, only finished a couple of years of college by the time she went at night as a working mom in her 50s. The math and science courses were, by that time, beyond her. She loved the literature courses most of all!