My view as an OT – not an educator!
Every child is different. Fabric types and also socks and shoes are often the biggest problems. Ties can be a big problem for some children. Tights can be tricky for some girls, so trousers are sometimes easier. Some children also struggle with hair cuts, I’m not sure how strict the current policy is for boy’s hair (and not sure if you can discriminate around this anymore?).
In general it’s helpful to have flexibility on fabrics – so a white shirt , rather than a specified brand, allows parents to then find a white shirt that their child manages.
Then, it should really be discussed with the child, get their views on what stops them from concentrating, and the parents.
In my experience, uniform battles can be the difference between a child coming to school and a child not – between a calm morning routine and a daily fight.
To me the goal is that the child is in school and learning what the need to learn. Once at university or work they can wear what ever they like, so clearly clothing doesn’t have a significant impact on learning. I understand there are reasons for being strict with uniforms but when there are sensory differences I just find it is one thing that should be easy to adjust which can make a massive difference.
So the policy should include flexibility with fabrics and trousers/skirts/haircuts and then have a case by case analysis for children with additional needs. If you’re seeing this is being abused, you could ask for medical confirmation e.g. doctor’s letter for eczema, occupational therapy sensory assessment for sensitivity.