In my school, we are allowed to bring in our own keyboards if we so desire. Granted, I'm the only one who does this, but they still allow it.
I have brought in multiple keyboards and nobody seems to mind, except that one time I brought in an actual mech.
I can't say this for all high schools, considering that I live in a rural area and everybody on the staff team is biased towards me, but hey. It's nice to have the option.
FYI, I have never had to ask if I could bring one in. I just do, and nobody really cares.