Your employer--whether private company or city school, and whether your boss is a manager, a business owner, or a principal--has the right to not allow employees who are leaving employment to go back to their office, room, desk, etc. and pack up their belongings personally. The employer must send you all your belongings--they can't keep them or throw them away--and if they don't, you could sue them; but it is legal (and is actually fairly common in corporate America) to not let the departing employee pack up his/her things him/herself. (It may be because they want the employee offsite immediately, and to not speak to other employees or customers--e.g. students--any more; it may be because they want to make sure you are not taking anything not belonging to you.)