I started recently to watch many clips of top pros in slow motion on Youtube. These pros, men or women, are the best teachers (or teaching reference) for techniques. You can tape your kids and let kids compare the video. It's truly amazing! One local coach charges $75 an hr doing the same thing. I should have done this 4-5 years ago. It's very hard to break a bad habit for a 16 yr old. We still take privates from a former ATP pro, who can hit balls to almost anywhere from everywhere - nice to confirm that he teaches what most touring pros do today.