Most of the transfers I know about don't work out. If they kid was good enough he would have made the team at the school he is at. About the only thing I know of that has worked out is transferring from a smaller school to a bigger school for the exposure of a very very talented player. Right now we have a 3A QB who transferred to my kids HS. We play in 8A (largest classification). We are a perennial football power house. Won states within the last 5 years, ran up to semi's two seasons within the last 5. Did not make the playoffs for the first time in 20 years last year. The team was OK, not good. In IL you need 5 wins to be playoff eligible our conference is very tough. A few schools are leaving because unless your in one of 4 programs you are pretty much guaranteed 4 losses in a season. Anyway, QB is very talented. Family moved to the district mostly so the kid can play football here. This years team is maybe a little more talented the last years, but lacked a QB. He will start here and will probably get the additional exposure he needs. In this case it made sense.
I have seen a number of other cases. More of them like this. They almost never work out. Kid is the starting QB and gets decent basketball playing time in Jr. High. Thing is the kids parents think he is a great player. In reality he is low side of average. In addition they live next door to the Jr. High heavy weight football coach. He also coaches the 8th grade A basketball team (highest level in the school). The coach has a reputation for having favorites regardless of skill set. Its true, I have a kid that was very talented and one of his favorites, so he got a lot of playing time, but I watched other kids with talent sit because the coach favorited someone else. Anyway, kid is starting QB in Jr. High. Goes through HS summer camps, gets 3 days into official summer workouts and the family realizes they kid is not going to start on the Frosh A team, let alone be a QB on the B team. Of course the coaches "don't know what they are doing". Kid transfers to a private school. Family did not research transfer rules, but in IL if you transfer public to private after you attend the first practice at the public school you need to sit out a semester. Kid is now sitting out football season and the first few weeks of basketball season. Dad is going around telling everyone, to wait until next year when we play you. My kid is going to dominate and prove the public HS coaches wrong. Next year rolls around. Kid is on the team but buried on the depth chart at a position other then QB. Didn't even make the basketball team.
I've seem more of the later example the the first one over the last 10 years or so that I've been involved with HS sports.