Board Thread:Questions and Answers/@comment-24520051-20171203215353/@comment-1257201-20180518235012

Sandy Hawkins was still a kid in all his Golden Age appearances. His first post-Golden Age appearance was in (1974), in which it was revealed that he had been imprisoned since the Golden Age. So I don't think he ever graduated from high school; maybe he never even attended.

Speedy was almost certainly out of high school by his heroin days in (1971). But he and the other Titans were all apparently in high school in 1966-1969, since their adventures at that time were high-school based, not college based (see, , ).

Robin graduated high school in (1969). Kid Flash graduated high school, and revealed his secret identity to his parents, in  (1978).

The character I have in mind graduated before any of these.