My son's current school is a Catholic one, and he is therefore not allowed to wear tracksuit bottoms, but has to wear trousers instead.
He has recently had a massive growth spurt, and has put on quite a bit of weight around his stomach area, and as a result most of the trousers I buy for him from the shops are standardised for a specific age group, but not very adjustable in terms of size, which often means even when I buy him trousers for an older age than he is (because often the waist is that little bit larger) the legs of them are often way too long, and I have to pay even more money (sometimes more than what I paid for the actual trousers) just to get them altered at the Tailors!
I often feel that I can't win, and that (even though they also sell elasticated waisted trousers) they still don't cater for slightly larger children.
This is one of the biggest challenges I face at the start of almost every school year.