You come across a lot of interesting posts on tennis forums I had to post this comment re coaching and juniors.The topic was addressing American Junior tennis and coaches.
I think it truly is the lack of proper instruction. From all I've observed US coaches are not correcting kids enough at all, and if they are correcting they do it once in a while and talk about it after. That is not how you do it imo. My son has trained in Europe and in any small club the coach will stand in the middle during match play and direct them constantly, demands corrections, power, even gets a bit angry if they seem to be losing attention or hitting poorly. During drills you need to be constantly correcting the technique, "elbow, up, elbow up, if you don't want to hit the net get that elbow up!" I know you shouldn't think all the time while training, but this becomes a reflex after a while with kids, and they no longer think about it, they do it. Here in the States, my son will play an hour without a coach saying anything(at a very good academy), likely not even watching. Why is this? Coddling the children(customer), afraid of confrontation, lazy, different teaching styles? I believe that complete difference in parenting is the reason, parents in Europe are not upset with the coach doing his job and usually will ask the kid, well what did you do wrong and here many parents will take the kid's side.
This is alive an well in this country and is a huge problem, technique is important but coaches all too well take an easy option , correct technique must be repeated over and over and over before it becomes natural , Parents look for other answers ..maybe a change of coach..coaches like to spin the yarn you need to do this it will come, you must be attacking ...well yes but if you have not the technique then your attack will turn to points ....for your opponent that is......Discipline is a huge factor and practising and repeating the correct technique is so very important!