I had a comparative religion section in my public Middle School social studies class, but in that we compared several religions. It was basically just a single research paper.
But even as careful as they were about it, my teacher still seemed to show some Christian bias. Like I wrote something about Jesus being the son of god and he put a little note next to it saying something like "no, he IS God.
And I made a note about how Judaism, Christianity, and Islam were kinda all the same basic "root" religions, they just splintered at certain points (bare in mind, I was like 13 so my analysis is about as basic as you can get) like Judaism+Christ=Christianity, and Christianity+Muhammad=Islam. And again the teacher made a little note like "yeah, not really" and that was it.
I remember a girl being really upset because she felt her paper was unfairly graded (I assume because she was critical of Christianity) and this was with our school being CAREFUL about tiptoeing around the line of teaching ABOUT religion and teaching religion. Just full blown allowing the bible to be taught in schools is just a bad idea.