Revealing mistake: At one point Charles Bronson wields a rocket launcher, the type which is a one shot disposable variety that comes pre-loaded with the rocket inside the launcher and it cannot be reloaded. The problem is, before he fires, he swings the launcher so the audience can plainly see there is nothing in the launcher just before he fires.
Revealing mistake: When Chang the driver is shot in the head, blood spurts out from his forehead a split-second before the gun fires.
Revealing mistake: The principal apprehends the two younger and bigger guys at once (and for some reason they don't gang up on him and kick his butt). The other guys in the Chevy decide to get back in and drive away. You can already see on the dirt the path they will follow, which is logical for the bit in reverse but not so much for the part when they turn left and go forward, which is not how the car could arrive to that point. And when later the car circles around, it moves also on a path that was not showing in the first shot. (00:11:50)