There has been a lot of talking of kindergarden redshirting, the idea that well to do parents hold their children back so that they start kindergarten older than their peers, so they do better, which builds confidence that stays with them their whole life. There is evidence in soccer that Euroepan football stars tend to be born in months that would make them relatively older for their peer group, giving them the advantage they needed to go to the pros.
This trend goes against my own experiences. Growing up in a fairly typical public school system, I always noticed I was rather average for my grade. Born in March, nowhere near the cut-off. But at MIT, among in theory high achieving kids, I found myself to be relatively old amongst my peers. For example, where I turned 21 mid way through junior year, most turned 21 after junior year, (R- for example).
My theory (perhaps since this is how my mom thinks) is that kids of helicopter parents are pushed at an early age, (I was doing multiplicatoin tables and programming computers before kindergarten), and so parents would want to start their kid early to avoid boredom and to get a jump start, rather than late. Heck, the mark of a high achieving kid was one who skipped a grade.
Not sure if this "red-shirting" is a new trend, or the sample of my friends is somehow biased.