Actually I fully believe that religion should be kept out of schools because of how divisive the nature of religion is. Even if I was a Christian, I'd still believe this and promote it. Because Jesus himself was against this sort of thing. He felt that religion should be a private thing. Here's the verses:
Matthew 6 KJV - Take heed that ye do not your alms - Bible Gateway
Even at its most benign religion is entirely divisive.
Because only the people who properly worship the proper deity get to go to heaven, and nobody else does, no matter how good of a person is. In order to get to heaven, you must follow the tenets of your religion. Nothing else matters.
Biblical support of this comes in this verse is in Mark chapter 10.
Mark 10 KJV - And he arose from thence, and cometh - Bible Gateway
If you want modern proof I can give you a link to a couple of you tube examples of how divisive it is.
School should be a place of learning and safety for children. But because they are a captive audience it makes them a popular target for people of any ideology to target and indoctrinate.
Schools should not be for indoctrinating children, regardless of the ideological or religious or political belief. It should be about reading, writing, and mathematics and college should be about job training.