The one I went to started doing this, I think.
I went there when it was a failing school, a new head teacher came and got it up to outstanding the year after I left, every year the children coming, compared to the year before them, were richer, more religious, less inclined to break rules, and seemed younger/less streetwise. My younger sibling still attends and I spent time their briefly as a transition assitant for a student with sen so I saw how it changed.
The drugs and police involvement died out with my year of students.
My year had 4 preganancies in year 11, there has not been one since I left. Attendance has improved, the children wear the uniform properly now and the school now has considerably more funding.
There are less fights and almost no instances of weapons being brought in, wheras these were regular 7/8 years ago while I was there. The catholic aspect has really ramped up, and the rules seem stricter. More students are driven in rather than walking, which I assume means they are coming from further away, rather than the two overpopulated estates that surround the school.
I assumed at the time, that this was a school getting better ofsted ratings, and the types of children that administrators want in schools started applying more. So each year the school took more and more of the richer and priviliged children and the others stopped making the requirements. So the 'nice catholic children' started applying and they didn't have to just take the local kids who didn't attend church.
As a student who was the last of the 'riff raff', it was weird, especially how much more money and resources flooded in once the younger kids appeared, and how lots of peoples siblings didn't get in anymore. It felt a bit like as soon as the school was actually good and there was money- they didn't want us anymore. All the local kids go to the next school over now which is a different 'satisfactory' comp.