Either this article is poorly researched, the study is scuffed, or both. It isn't the uniform but the type of which that the school enforces. There are plenty of schools with gender neutral uniform policies, heck the one I went to in Aus had 3 options, one of which is sports specific for all genders.

[–] Wilshire 12 points 10 months ago

The last paragraph

Sarah Hannafin, the head of policy at the school leaders’ union NAHT, said: “Physical activity, PE and sport are an important part of the school day and curriculum for pupils. Schools do much to help ensure all pupils are healthy and physically active and break down barriers to participation, including among girls – and this includes considering the uniform choices available for children.”