The Impostor(1984)

After being released from prison, small-time con artist Cade tracks down his old girlfriend. When she rebuffs him, he fakes his past in order to get hired as the principal of the school where she teaches, in the hopes of winning her back. Cade soon begins to take a sincere interest in the welfare of his students, and enlists the help of his friend Matthew to break a drug-dealing network that has infested the school.