@barbie, the rule where I live, my friends told me, the gender you present is the washroom you use. When I dress female I always use the ladies washroom in public places. No asking you just do. As you say all students know who you are, they should know you wouldn't do anything wrong or it would jeopardize your job. You dressed as a Lady can be troublesome going in the men's washroom.
Back on topic as I don't want to move this off topic.
Jamie