This week, while catching up on trash TV, I came across the second episode of A Very British Airline, in which eager trainee air hostess Jodie had her contract with British Airways terminated for not reapplying her lipstick enough. It was a depressing turn of events. The cameras had followed her closely through the first couple of episodes, with the clear intention of showing her graduation at the end; the decision felt monumentally unfair.

The episode came back to me when I read this morning about draconian headmaster Rory Fox (previously a teacher in a prison) sending 250 girls out of lessons at Ryde Academy for having skirts that were too short or trousers that were too tight. Boys were also sent home for flouting the uniform policy, apparently for wearing shoes that were not made of leather.

I have never been a big fan of school uniform – some argue that it levels the social playing field for poorer students, but I don't find that very convincing. If people are all in the same faded red jumper and ill-fitting grey trousers, it is reasoned, there is less room for judgment than if Lizzie fails to own the same Armani jeans as Beth. But publicly humiliating boys for having cheaper, non-leather versions of the generally accepted black school shoe, potentially takes some of the power out of that argument.

The state sixth-form college I attended had a nonexistent clothing policy – many of us took our A-levels in pyjamas without a teacher batting an eyelid – and a track record in results that rivalled the nearby private schools. At one of those private schools, my teenage boyfriend was being harassed, repeatedly, about his haircut by a cohort of adults. At one point, the headmaster of this prestigious institution was left with his head in his hands by the very idea of a (clever, well behaved) young boy whose naturally curly hair went slightly past his ears. Suspension from school was seriously discussed – even expulsion. He was a straight-A student. It was utterly absurd.

While both boys and girls can find themselves on the wrong side of the school uniform law, there is a difference in how they are treated. What counts as "smart" for girls all too often hinges on how revealing their outfit is deemed to be: in schools such as Ryde Academy, for instance, clothes must not be "provocative". But which teacher is it who goes around making the judgment call on whether teenage girls' trousers are excitingly tight, rather than just straining a bit after an ambitious lunch?

Fox has said that in enforcing school uniform policy he and his teachers "are conscious that we are preparing students for the world of work". But, of course, as Jodie's experience with the lipstick shows, the rules for women aren't ever simple. Girls and women are expected to tread this careful line – appealing but not revealing, pleasingly pretty but not sleazily sexy – from a very young age. It starts with a teacher telling you that your trousers hug your adolescent curves too snugly, and it ends with a sweaty-faced man in a straining white shirt telling you, irony of ironies, that you've lost your job because you "don't look the part of an attractive customer service team".

If we want to enforce uniform policies – and I'm still not convinced about their use in schools – then we have to apply sanctions equally to boys and girls. Otherwise, you're just needlessly sending 250 girls away from the one place that might have educated them into being able to call out sexist bullshit.