https://www.trutexbtru2u.co.uk/research-shows-wearing-school-uniform-helps-reduce-bullying/
This is a recent British study focussing on bullying. Teachers, parents and children themselves see the differences.
https://eric.ed.gov/?id=EJ1255002
This is an American study that focusses on the students and parents and reaches similar conclusions.
Both studies focus on the perception of the issue, not on hard numbers on bullying. What I was looking for are, if cases of bullying drop when school uniforms are introduced.
I mean, can you get hard numbers on bullying? It’s not a black and white situation. If someone feels that they’re being bullied then they are. The American study shows that pupils feel that there’s less bullying. If you want to design your own study then you can, but I’m not sure how.