I am sure you trust your son. However, teenagers are the world's best at manipulating their parents. You have been told that the headteacher said that the letter was pathetic. Personally, if you wish your well-behaved, well-performing child to stay at the school, I would give the man the benefit of the doubt, assume your little darling has embroidered the facts, pay up and make your son do some chores to earn the money to pay back for the tie. You are right that causing trouble is not a good idea. If your son is generally happy at the school I would let this one go. A wee chat about vandalising his uniform wouldn't go amiss. What others are doing is irrelevant. However, if you are absolutely convinced that this has all actually happened you might get in touch with the governors. It may be that other parents have had similar things happens and yours could help the body of evidence against what seems like overbearing and bullying behaviour. Headmasters are not taken on for their ability to blend in they need to be strong and lead. Sometimes they get above themselves. sorry this is so wordy. Hope it helps!!! Just my opinion of course.