I think adjustment for Summer borns is a good idea.
The evidence is very clear. Summer borns do less well.
I think one of the main factors is expectations. In the early years, when age matters enormously the expectations of teachers, parents and pupils begins to set. Ideas are formed as to who is able and who is not. Ofetn without recourse to age! This can stick.
I have summer borns (and prem to boot) and I took no prisoners on this. I made it abundantly clear to everyone and anyone that they not entitled to peg my DC's ability without reference to their age.
Consequently they were always considered perfectly able for their age. Now as teens they are simply considered able...