First off, there are many interpretations of what "classroom supplies" means. My guess is that many if not most dedicated teachers at every level including post-secondary buy many supplies out of their own pocket. School boards differ and individual schools differ in terms of what is reimbursed and what they have the money to reimburse. Teachers differ in terms of how many hoops they are willing to jump through in order to get reimbursed. The list of items that I have bought that were not reimbursed is very long. My guess is that buying the things you need without reimbursement is true to a certain extent of most jobs. It could just be that, in schools, you need enough for every kid in the class - not just something for yourself (like new ties, or whatever).