I'm running into this too...the part about this "they can not reliably reproduce the basic IR arm action" -- All I can do is look for glimpses into proper technique and encourage it. For example: can she at least get on the side of the ball coming down past 9:00? I charge them the beginner rate, and just keep working!At the end of the summer I volunteered to help with the pitching for a local 10U startup for a travel organization. I knew the parents of some of the kids. At the first practice the coaches asked who wanted to pitch, 10 of the kids raised their hands. I took them to the side in pairs, I demonstrated 'lock it in' and had the girls throw into a fence while I watched and gave them pointers. I selected 5 of the 10 girls and I went to the first hour of the Saturday practices to work with them. I had to 'cut' one of the girls because she couldn't even handle 'lock it in'. I worked with these 4 girls for 6-7 weeks doing very basic IR drills. All four asked for private lessons, one dropped pitching after 2 weeks. I've had 5 lessons with 2 of the girls, about 8 with the other one. Two of the girls are 9, one is 10. So where do they stand now, not good, they can not reliably reproduce the basic IR arm action which, for me, is the one nonnegotiable in pitching. In years past I have had several other 8-9 year old students with the same issue. This is what makes me think that there is a certain level of physical development that must be reached before a child can learn to pitch.