I think it’s also important to point out that there are distinct regional differences. My son who we “held back” at K turned 15 at the end of June and was always the oldest in both a small private school as well as LPS here in CA. That being said, we were quite surprised when we were told that there were many boys older than him in his dorm. In the west, folks would never consider having their child repeat a grade in 9th or 10th grade despite entering a new, more academically environment–nor would they even consider it for athletics! No one repeats past third grade where I live, even if they are having academic difficulties (sadly the school’s keep pushing them through). The idea of voluntarily repeating a grade in high school was completely foreign to me until this year.