This. My older kids have birthdays later in the academic year but have ended up in groups for more advanced students.

Mind, nursery was a complete wash when it came to academics -- learning to count to 3 when you can already count to 20 is rather futile. Public schools just can't tailor to individual students.

Socially though, nursery was well timed for them IMO.

That's a good point yeah. But I think when I said that younger kids didn't do as well it meant both in terms of ranking (they were in the lowest percentiles) which indicates that they don't do as well as their peer, but also in terms of future opportunities to attend college or university.