The private schools often require a recruited athlete to repeat 9th grade. They believe the kids haven’t been challenged academically in the past to what they will experience at a high academic private school.
i know a kid who went from public school after 9th grade to Catholic school repeating 9th grade. He had an August birthday. I believe it helped him athletically. Plus he was now in the same grade as all his baseball buddies. The LL deadline used to be 7/31.
Someone mentioned physical and emotional maturity. I started school at four years old. I was supposed to be a boy genius. My parents overlooked one thing. By 8th grade I was very physically and emotionally immature for my grade. The treatment I got from older kids (everyone was older) starting affecting my desire to get up and go to school.
We moved after 8th grade. My father decided to have me repeat 8th grade. I fit in. I returned to getting all A’s. I went from being a kid who made the lineup in sports to a dominant player. In any aged based rec sports I had always been dominant in my age group. A year makes a big difference before growing and filling out.