Having spent my career in education I can tell you that schools spend a lot of time making and enforcing rules with the very best of intentions but end up tying themselves into grossly complex knots.
I suspect that the reason for the leather shoes rule is that your teachers don’t want to see students competing over who has the most expensive and “in” trainers. I would suggest that you google “faux leather shoes” to see what is available (and there is a lot). Once you are kitted up you have a choice of approaches.
The easier one is to then say nothing and I can almost guarantee that it will never be noticed or commented upon. The second, once you are settled in and if you want to make an issue of it, is to approach a teacher you think might be sympathetic and explain what you have done and you will probably eventually get the rule changed to “leather or leather-like”. It would be even better if you could find a comrade in arms to help with the latter approach.
Upper schools are usually great places to be. I hope you have a good time!
I would buy nice but obviously not leather, canvas shoes and fight this rule, which is discriminatory against vegans, if challenged. We should not be forced to even appear to wear the skins of deceased animals.
that is a really thought mate to no support to the slaughtering of animals to get products for our benefit. This is quite normal that schools would require their students to wear leather shoes during school hours.
I would give a thumbs up to the suggestion that "Emma JC" gave you. You can arrange second-hand leather shoes for yourself, I know it won't help much but this way you might feel less bad.
Or you even have shoes which are made of like cloth (don't know the exact term of the material though) if your school accepts so.