To express your religion in school could come from two different perspectives. If you mean a student telling people about their religion, then yeah, there's no reason they can't exercise their right of free speech and talk about it.
If it's a teacher it gets a bit tricky. I'm not an expert, but I think it's up to the individual professor whether or not they want to share what they believe in, but if they do, I don't think they should endorse it, just mention it once and move on.
Religion like science is theory or a guess on how our universe works. We use theories to help our limited minds to comprehend how we exist. I think everyone has a right to express their theory to the general public. To explain my stance better here is an example; In school students shouldn’t only learn about Evolution, However the same goes for creationism or any other theory shouldn’t be the only thing taught to students. I feel the need to say that students need to choose what they believe and do not believe, by being bias to one side takes out that amazing principle of self-uniqueness.
Personally this whole Atheism vs. Religion thing is complete bull because to me both are about people control and trying to make everyone think and act a certain way.
I think we should be able to express religion in schools. What I am against however is trying to force that religion upon those of other faiths. We all have the right to hold on to our beliefs without the worry of other people forcing their religion upon us. We have both of these rights as human beings.
I wouldn't really know about other people introducing a new religion to you at school since I go to a Jewish private school, but in most cases it's okay. Sure a student can tell another student about his religion. If a teacher does, it depends how. Forgive me if I'm wrong, but I'm pretty sure most public schools do stuff for Christmas and other holidays no matter what.
Individuals should be free to practice their faith in schools, provided that they are not disrupting the class or coercing others to join them. The US Department of Education allows students to pray of their own accord in schools and gives guidance as to how schools should act to both protect the right of students to pray and also to prevent abuse of that right.
If you are going to allow gay pride to be demonstrated, why would you censor the religion of others? It is being hypocritical, and frankly idiotic. If you are going to give one group a right to express their opinion, and not another, that is discrimination. So, regardless what you think, if we are to have equality, religion should be able to be expressed as well as gay pride, atheism, pro-life or pro-choice. Should we expel interracial couples? Excluding their right to have a relationship is just the same as excluding a religious person's right to a belief, and it possibly being taught by a religious teacher. I am not saying they can present their religion as an absolute truth, but rather an alternative. Just like Darwin did with his hypothesis on the origin of species.
People who wish religion to be allowed in their school make one big assumption, that the only religion would be their own. In private schools, this would be the case because the students would be among the same religion but public schools consist of people from all religions. Any expression allowed by one religion would have to be allowed to all others. Many times, an expression leads to curiosity of others. People may ask this person about the religion and find it more attractive than their own.
Hypothetical situation: A freshmen in high school who was raised to be Christian meets a person wearing a Wiccan Pentacle. The freshmen asks about it and this leads to a conversation about Wiccan. Over time, they become friends and the freshmen's interest in Wiccan grows. Next thing you know, the freshmen tells his parent that he is leaving the church and becoming a member of the Wiccan faith. This is just one of many situations that not only could happen but would happen in just about every public school. This could also happen with other religions too like Muslim or even Satan worship.
Thing you have to remember is if you open a door for one religion, you must leave it open for the rest.
It is fine to tell your friends about your religion however if you end up challenging their beliefs that is where I draw the line. I remember this one day at school were I was trying to pay attention yo the teacher. These two kids were talking very loudly and very angrily. One of the kids was so upset in the discussion he was on the brink of tears. The other kid claimed that he was not a real Christan. I told them both to shut up. The kid who was challenging another kid's religion told me there was a place for everything. That place is not school. I told him this is not a theology class. At a young age kids may not understand these problems. It is alright to express your own religion but once you step into another persons religion that is when things may go sour. If it is a debate meant for religion that is fine, but come on, just respect others beliefs even if they are wrong.