Burford School pupil Christopher Brunt lost most of his school work after thieves broke into several cars at the school on Friday evening.
Christopher, 14, of Eton Close, Witney, was staying with a friend overnight and had left his school bag with his father, Roger, who is a teacher at the school.
Christopher's grandmother Pamela Hawker, of Pens Close, Witney, said: "We are appealing for its return. I don't think the thieves will want a bag of school books and they may have dumped it.
The cars were broken into between about 7pm and 8pm.
There were people about as the school was holding a fund-raising dancethon."
"Christopher is very upset as he has lost a lot of work which he needs. The black bag carries the name Mizuno."
Anyone who finds the bag should call Burford School on 01993 823303.
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