The Substitute 4: Failure Is Not An Option (2001)
The Substitute 4: Failure Is Not An Option is a 2001 action film. Starring Treat Williams once again as Karl Thomasson who is now an undercover policeman that must infiltrate a military school's faculty to cease the actions of a white supremacist cult. This was the last entry in the popular "The Substitute" series and was released direct-to-video.
More at Wikipedia.