How are teachers supposed to teach Intelligent Design at schools?

I would suppose that it would be fair for the school to support and teach curriculum that coincides with what the parents who send their kids to school believe, otherwise it's shoving your beliefs on other people. If the parents are atheists--fine, don't teach intelligent design or whatnot, but if the parents are Christians or other religions, let it be that there are teachers that will teach bible or whatnot.