My dd is also very different at school. She hides who she is at school. She says she doesn't like to be "seen" by people. She would rather blend quietly in the background whether socially or academically. At home she is a bubbly bouncy quirky kid, but at school she is all smiles & agreeable to everyone to avoid conflict or standing out. I would ask the staff what they see at school. If she is anything like my DD they may answer absolutely nothing looks out of place to them.
I felt the same way watching DS sit on the playground with a book all year rather than talk or interact with peers. He really was fine with it. He really did see peer relations as a waste of time in his younger years. The boys all wanted to play sports or other things he had zero interest in. They often didnt know what he was talking about when he did bring something up. I took opportunities as they came to encourage his social development over the years. He is still isn't always comfortable in the group setting but he functions well in it. He does better at the high school because his peers are older and have more common interest with him. Although he was fine, it always left me feeling a little sad for him.
