I believe you can actually get them to sit out of religion classes in secondary school if you want, but on the other hand it's an easy A. In my school we were taught to argue our own opinions on issues so you could have argued pro gay marriage and pro-abortion and got full marks as long as you had resonable arugments. You also were supposed to be able to present the opposing arguments so you had to understand why people believe the opposite to you, I thought it was a good exercise in debating and listening to opinions of others. The teacher would try to influence kids' opinions yes but most will form their own beliefs based on wider social influences. The rest of RE centered around memorising Mark's Gospel which is also used in the Protestant religions.