I understand where you're coming from. A lot of people have said 'don't ruin the dream for her.' Well, what about ruining her whole senior school life by giving the bullies (yes, they are unfortunately in every school) ammunition to tease her about? My mum tutors a boy who is quite immature, but really sweet, and she advised his mum to tell him the truth before secondary school. His mum has, and he's totally fine, and still loves Christmas as most people do whether they believe or not. If I were you I would let her have this last Christmas - yes it is magical when children still believe, and then tell her in about February or so. Start by asking her about what she thinks. Get all cosy on the sofa together and ask her what she thinks about Santa. It could be that she'll say 'I know you just get someone to dress up as him.' If so, that's a good way to start the conversation about yes, it's just a game of pretend that grown ups play because they know it makes children really happy. Talk about the history behind Santa (St. Nicholas) and how now it's a time to try to make other people happy by giving them gifts. Explain how it made her happy to believe, so it's important she doesn't let her brother know the truth yet as he's younger and it's only fair he should be allowed to believe as long as she did. My mum's family had a nice tradition. There were 4 children and she was the oldest - every year whoever didn't believe in Santa would be allowed to stay up late and decorate the Christmas tree (they didn't put it up until Christmas Eve) - that was her parents way of bribing them to keep quiet about Santa not being real. If they had told they wouldn't have been able to help decorate it. I think that's a lovely tradition and I plan on using it when I have children! If you decide you don't want to spoil the magic and not tell her, then make sure you tell her not to mention Santa next year at school or it's sad, but she probably will get laughed at.