http://tvnz.co.nz/national-news/early-teens-forgotten-years-school-report-4962932
At first I thought this was some new wider study rather than ineptness on the part of schools here. However, this thread is about that non-existent study.
So, how much do we think that these years matter (13-15) for a child. The other way of doing it is the fifth to last and fourth to last year if school. (So if the last year came first in a race Y9 is in fifth place.)
I have limited time so this OP won't be very fleshed out. Personally I don't think Y9 matters that much. All one does is get used to the new school, really. Y10, however, really decides where you end up in Y11 so it is very important in terms of where the pupil can go.