I haven't reviewed this material yet, but I believe the answer would be as follows:
If X grants to Y for life, and then B so long as B uses the land for a school, and if not to C.
B has a vested remainder subject to divestment. B will get the estate when Y dies unless he fails to use it as a school. It will vest to him and stay with him if it's used as a school and he has control over the matter. B doesn't have to do anything but wait for Y to die and it will be transferred to him. If, however, B fails to use the premises as a school then his interest in the property will be divested to C.
C has a contingent remainder. C's ownership of the property is contingent on B using the property as something other than a school. If B doesn't use as a school, then C gets the property.
That's the best I can explain it and I think it's right. Property is a real female dog.