i'm 15 but and im suposed to be in 3rd grade but let me explain

if you become 4 after 1 october you cannot join the schoolyear that started in early september. but most parents just let their child join and then the school makes m redo the schoolyear (for psycological reasons). i on the other hand didnt had to redo the schoolyear but could continue right away. i became 15 on 12 october this year, but im in a class with people that become 16 this year.

So i'm supposed to be in 3rd grade but im in fourth