When my daughters took their GCSE exams a letter came home the week before, reminding all the candidates that although they were off timetable they were still 'at school' and full, correct uniform was to be worn at all times. Of course some of them tried to 'bend' the rules and turned up with forbidden items of jewellery etc - they were told to conform to the rules or be excluded from the exam! They soon complied with the rules