I'm looking for a movie from the late 70's or very early 80's. A group of about 5 or 6 men kidnap an entire grade school (very small one out in the boondocks) and the lone teacher, put them on a bus, and take them to a cave out in the middle of nowhere. They have surrounded the cave with a ditch and filled it with sharpened branches, kind of like a deadfall. After some time, the teacher and students fight back and begin killing the bad guys.
Please help.

Might be Fortress

Thank you, you da man!

Glad to help.