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Horsemad, I think I would go and see his teachers about his results (perhaps there is a parents' evening coming up). If they are really that good then perhaps he is brighter than you thought and doesn't really need to revise that much. If they have been exaggerated to encourage the students, then he needs to know that (and so do you) so that he does the necessary revision for the real things.
In my experience schools tend to come down harder after the mocks to shock the students a bit, but that may not always be the case.
Whatever the outcome, I wish you the best of luck as it's a stressful time.