Our local secondary school, that all three dses went to, has a very sensible uniform policy - black or dark grey trousers or skirts (skirts should be a reasonable length), white shirts, black jumper or cardigan or fleece or zip up sweatshirt - only stipulations being no hoodies, jumpers to be v-neck, and cardigans, zip up fleeces/sweatshirts to be undone enough to show school tie. Black shoes. Wellies or boots on snowy/wet days are fine - just change them at school. If there is an unavoidable reason why they can’t wear their school shoes, send in a note, and it will be fine.
PE uniform is shorts/joggers and t shirt with optional fleece - any colour or design as long as they are not football branded/strips.
This is a complete contrast to the grammar schools ds1 and ds2 went to before we moved - uniform including a blazer - in ds2’s case the blazer was dry-clean only - and special PE kit that could only be bought in a few places. The who,e thing cost a small fortune.
And do you know standard of education at the grammar schools and the local secondary here are pretty similar. When we moved ds1 went into S2 (the Scottish equivalent of Yr 9), and ds2 was in S1 - so they did all their public exam courses here, and we are sure they did as well as they would have done at the grammmar schools.
Behaviour in all the schools was good too - I don’t think the more relaxed uniform at the local school made for worse behaviour - in fact a single bullying incident at the local school was dealt with swiftly and very effectively, whereas ds2 was bullied for more than a year at his grammar school, and they did little or nothing about it. And it was at the grammar with the expensive PE kit where ds1’s whole kitbag was taken, and the contents spread around the school for a ‘joke’ - nothing like that happened at the local secondary.
All of which is a very long winded way of saying that, in my experience, a strict uniform policy doesn’t necessarily mean the education offered will be of a higher standard than the education at a school with a more relaxed - and sensible - policy.