Creationism deserves equal time because evolution is only a theory. But a theory in the scientific sense of the word, meaning that it explains a wide range of phenomena and that there's lots of data to back it up. Science classes are suppose to teach science. The theory must be testable. Evolution is, in that there can be things specified which, if they can be verified, would disprove evolution.
Creationism allows no such test.
Creationism does none of this. Evolutionists themselves admit they have no proof. Science doesn't deal in proof. It deals in evidence. Evolution has LOTS of evidence.