First of all you would need a thesis statement. In this case, you would have to either argue that there is a role or there is not a role for religion.
If you say that there is a role, then you will have to give reasons for this position. you may want to argue that religion is part of our collective history and so it should be taught. Or you may say that people should be given the freedom to teach religions as long as other religious are covered. The point is that you need reasons to back your thesis.
If your thesis is that religious should not be taught in school, then you need reasons for this as well. You might argue that there should be a separation between church and state and this entails no religion in public schools.