Automatically assign user to a profile term / taxonomy term?

Hey all,

I'm building an online course website where I would like users, when they register, to be automatically and sequentially assigned to an "instructor" (that is, user 1 assigned to instructor A, user 2 assigned to instructor B, etc. so that each instructor has roughly the same number of students). Is there a way to do this with a simple profile term? Is it possible to do in organic groups or user tags?

Thanks for your help.