Religion has no place in schools outside of clubs or student-led-and-organized functions. Students should not receive any sort of academic credit for exploring parts of their personal lives and beliefs. Students have churches (or an equivalent) and their home for those kinds of studies.
As for trying to taking it out and going to an extreme of where it can't be mentioned or expressed is also absurd. Students and teachers (teachers to a lesser extent for semi-obvious reasons) should be able to express their religion as long as they're not advertising it or using social pressure to coax others into uncomfortable situations.
The problem is, at what point does telling become brainwashing?
When someone (children specifically) says they don't want to go to <insert religious function / building here>, and they are either told by an authority figure that they don't have a choice or they are disillusioned into thinking they have an option, but are heavily pressured by said authority figure and peers into going and may face heavy social stigma from choosing not to participate.
Slightly off-topic, I also don't want religion being taught in school due to the stigma that any religion may get as a result. Atheism, for an example:
This may clearly be propaganda, but it brings up a good point. It would end up being taught favorably in one or another religion's name. Also, in an instructors failure to maintain a mediator's standpoint they may influence how a religion looks, either subliminally bashing it or making it look good.