Monster Jedi, you seem to have taken this debate way beyond its remit (and your actions seem questionable, indeed reprehensible; a thinly veiled threat of violence towards the headmaster is setting a good example to your kid?).
Back where we were, a child was denied the opportunity to take an exam, the result of which potentially affects the rest of his life, because he has the wrong footwear on. Whilst the child was maybe daft to breach the rules, application of a bit of common sense would not have gone amiss (Coggy, is that on the PGCE training?!
). As Graham pointed out, a quick 'don't do it again' would have enabled the kid to take the exam and marked his card.