Your head teacher has to make sure that pupils wear the uniform which the governors have chosen.
The law allows them to dish out punishments, like detentions, to kids who don't follow the rules.
Teachers are supposed to be careful and find out in private if there is a reason why someone is not wearing the right uniform.
There might be a reason like their parents can't afford it or they could have a medical problem.
No one should be made to feel uncomfortable or discriminated against because their parents couldn't provide them with the right school uniform.