I visit 40 schools a week. Some of them keep my ID. Some don't. The reason for those that do is they want to make sure I check out. By December, most if not all will quit even asking for my ID and just print my sticker as I walk up to the door because they and the officers on campus will know who I am.
Pick your battles. This isn't that big of a deal unless you are checking in during school hours and not leaving until after the front office is gone and locked up.