Designate either the coach or one of the students to be the "thrower".Two players stand side by side with their backs facing the thrower. On "go", the thrower will launch the frisbee over the top of the players heads and they must anticipate where the frisbee is going and try to get to it first.
After a few rounds of practising the activity you can introduce a points reward system, the player that catches the frisbee will be awarded one point.