Religion is something which many people feel very strongly about. Some parents may put their children in a school associated with a certain religion or denomination, because they want to make sure that their child shares their views. Other parents are not so strongly minded about religion and others have no religious beliefs at all.
Schools nowadays have to teach religion but with a more encompassing perspective. The do not just teach Christianity but other religions as well. This means that it is more inclusive, for those children who are not Christian but it also means that children understand about the beliefs of other cultures which can help them be more well rounded and understanding of others. It also allows them to have the knowledge to make up their own mind as to whether they want to believe in a certain religion or not.
Some parents choose that their children should not attend assemblies because they have a religious viewpoint that they do not agree with. However, these days assemblies tend not to be a religious affair, at least not all the time. They might be a chance to share the achievements of certain pupils, discuss issues or share stories. Therefore, if you do want to keep your child out of assembly on religious grounds, it might be worth having a discussion with the school first about what they actually do in their assemblies.
There will be some teachers which have certain religious beliefs and these will be passed on to the children. However, as parents you do have more influence and so if you want the children to think in a different way, then it is up to you to make sure that they understand other viewpoints as well as that of their teacher. Teach them to question what they are told and they will start to have a better understanding of why they think that way and why it is different to what they have been taught to believe. It is important for them to know about religion so that they have the opportunity to make up their own mind with regards to what they believe in themselves.