It used to happen at my school.
We have 3 class intake and until the rules changed a couple of years ago classes were divided by age.
About 2/3rd of the intake started in September, making up the first two classes. The younger children, born Marh 1st or later started after Christmas - comleting the 2nd class, and making up a 3rd class.
They stayed like this until the end of infants - I think the next schol shuffled them for juniors.
However, it did mean that expectations for the younger class were often a bit lower - and tbh it didn't really benefit them. They started later, had less time in school and some even joined a pre existing class who already knew the teachers, each other, routines, etc. And this really affected them throughout infants and into juniors.
We now have one intake - in September. But all children can defer starting until term after their 5th birthday through parental chice In ractise, at our school, most choose not too.
It may be coincidence (we have made other changes throughout school in that time, as schools do) but expectations, pupil progress and actual attendance has increased for all children, especially summer born.
Summer born children still remain a focus/target group, along with other groups use as EAL, boys, pupil premium, etc. so they are carefulyl monitored every half term - but at present the gap between summer born children and others has narrowed a lot at our school.