How do I teach my kids to stand firm in their faith at school?

My oldest is in 4th grade and starting to ask questions about why our family believes different things than some of his friends' families. I want him to be confident in his faith but not judgmental or weird about it at school. How do you guys balance raising kids with strong Christian values while also teaching them to be respectful and kind to people who believe differently? Don't want him isolated but don't want him wavering either.