You definitely cannot teach people to be accepting of others. However, a school should force them to be civil and even pleasant toward all people during school hours.
really? on what basis do you make that claim? being accepting of others is the basis of our society. (we can't have a society if we don't learn how to accept others in that society)
claiming that this can't be learned is defeatist, and decidedly not helpful.
on the other hand, i don't believe you can force behavior on people against their will. they need to learn the behavior so that they actually want to behave like that.