Students are normally equipped human females. Their purpose in being accepted into the school is that they are prime specimens of Earth women, not so they can shag the other students.

No dickgirls, herms, transexuals, shemales, one legged hunchbacks or other exotics. The Headmasters at least examine every potential student before recruitment and they are traditionalists. They like all the right bits, in the right places, with the right shape and the right degree of elasticity. And no extras.