In our town there are three grammars - two single sex (boys, girls), and a co-ed.
The single sex girls school is 60-70% South Asian, in an area where South Asians make up approximately 15% of the population. Genuinely, well done to them and their families for helping their children to achieve the grades.
However, a lot of white families are choosing the co-ed, not because of racism, but for something a bit more complicated. Some white families who have sent their children to the girls' school report that a groundswell of the South Asian girls are not allowed to go into town / have sleepovers / mix outside of school, so it becomes cliquey with the South Asian girls seeing each other within their communities, and then limits the white girls to being friends with the maybe 6 other girls in their class - whom of course they may have very little in common with. Additionally when fallings out naturally occur, there are fewer options to hang out with a different crowd instead.
So it becomes self-perpetuating. Interestingly the co-ed more or less represents the town in terms of ethnic make-up.