The Substitute (1996)

After his fiancée, a teacher, is brutally attacked by a gang-linked student, mercenary Shale goes undercover as her substitute at a Miami high school. While posing as a teacher, he uncovers a dangerous drug ring operating within the school, tied to a local kingpin. As tensions rise, Shale fights to expose the criminals and protect the students, turning the classroom into a battleground for justice.