There is also a strange statistics with baby borns in early January and late December. There is a high spike of births in early days of January and a strange hole in births in the last days of December.
My daughter is usually the youngest kid in class (born middle December - here we put babys born in the same year in the same class) and usually has trouble because she is not as developed as kids born 11 months earlier - this difference will be less noticeable later in life, but know when she is 6 years old it is a bit sad.
I knew someone who came to the US as part of the Vietnamese boat people and his parents chopped a year or two off his age so he could start in kindergarten (and he didn’t know his actual birth year 30+ years later).
The result appears to be consistent across countries with different cutoff dates.
For example, British Columbia with a December 31 cutoff date.
Like in Norway, everyone born the same year go to school together, even though the school starts in September. (Which confused me a lot when reading Harry Potter as a kid, as some dates there didn't "add up"). We segregate sports teams that way as well, making it often better to be a jan/feb kid, as you're always the biggest/strongest, and thus get the extra attention, training opportunities etc, so a bias towards those birthdays in our sports.