I agree that the public school classroom is not the place to sway students toward one religion or another.  As an English teacher, my classes learned about many different religions.  I tried to keep the topic relevant to literature and culture.  It is important to know about many religions to have a well rounded understanding of our world, but teachers should not show bias toward one religion over another.  I we have to be careful with activities that can be uncomfortable to some students, such as your example of singing a hymn.  I did sometimes show video or ask students to listen to religious activities (such as monks chanting) just for the experience of it, but I would never ask them to participate in a religious activity during class. 

The restated basis of this discussion reflects the reasoning behind the separation of church and state, as included in the Bill of Rights - the first of the ten amendments to the Constitution of the United States. The Founding Fathers were so concerned about insuring that there was no development of a state religion that some individuals, and some states, ratified the Constitution only after it was agreed that a set of amendments would be promptly submitted for addition to the document, setting out specific concerns and procedures to absolutely guarantee individual rights.

So cuyler, your argument is that advocacy for any particular religion is inappropriate in the classroom and the practice or presentation of religious rites, performance of religious music (for religious purposes) and things like that are also inappropriate. 

This is much easier to agree with than your initial argument, which you have amended. 

There is always going to be some grey area as to what constitutes religious advocacy, but beyond that I agree that if the school is a secular school the educational experience for students should be free of religious persuasion (which is not to say that religion won't be discussed in context, but that it will not be advocated in the classroom). 

As an English teacher, I find that religious texts and an understanding of a variety of faiths is an asset to study. That said, now you have clarified your question, I agree that influencing students to favour any particular faith is not ethical.

I agree with #2 above in that the religious belief of a people is important in gaining a complete understanding of that culture and their actions.  With that being said, it shouldn't be used to influence students in a public setting.

I don't agree.  I teach history and I talk about religion all the time.  You can't possibly study the history of a country like the United States without talking about religion.  That goes for the histories of countries in Europe where things like religious wars were so important.  

I agree that people shouldn't be taught to believe in a religion, but it is impossible to teach various subjects without talking about religion.