Fight Back to School (1991) on Netflix

Plot summary

Chow Sing-sing's place in the Royal Hong Kong Police's Special Duties Unit is in doubt after a training drill in which he disregards his teammates. A senior officer, Wong Sir, instead sends him undercover as a student at Edinburgh College to recover Wong's stolen revolver. Sing is paired with Tat, an aging detective whom the school files list as his legal guardian, and he struggles with the schoolwork. On his third day, a cheating charge on a Chinese history test nearly gets him expelled, and Miss Ho, the school's guidance counselor, offers to tutor him herself. The school bully, Johnny, challenges him to a fight on the school rooftop, and only his classmate Turtle Wong takes his side.