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Hi Prickly, I'm a piano and violin teacher and this happens to my students all the time! I would contact the exam board and ask for a change of date/venue, I've always found them very helpful. It might be he's fine to do it in the first week though, so maybe check with his teacher first - many people ask for the final week so it gives them more time to prepare, but sometimes suddenly having a more immediate goal can focus the mind more when it comes to practice etc, and then the thing's done and achieved without dragging on!