I feel that humans would be at a severe disadvantage when facing off against dragon shifters in school yard brawls unless the school's faculty allowed the human students to carry military grade weaponry or giant crossbows. To mitigate this imbalance, I propose that the ability of dragon shifters to transform be sealed when they are within the school grounds. The school grounds are very large. I'm starting to get a Hogwarts like feel from this. Anyways, I think it's best that you should still quite easily be able to tell the difference between a dragon shifter in humanoid form and a regular human. One can imagine that dragon shifters have horns, reptile like eyes, vestigial wings, scales, tail, or retractable claws on their hands and feat in their humanoid forms -at least one or more of these traits or any other physical abnormality you can think of. Dragons are a diverse bunch.
Just something worth considering.