When it comes to instructors/coaches, I am VERY open minded. Yes, I may not learn a lot from one person, but I am open to learning AT LEAST one thing from every coach I have ridden with either them being a very professional coach or not.
When looking for a coach it is important to make sure they are CERTIFIED and have insurance as well. Anyone can "coach" someone to "ride", but if the instructor has taken the needed courses and mentoring hours to become certified, I would more then certaintly trust them more, not saying that there are instuctors that airn't certified that I wouldn't trust though, just IMO.
Yes, group lessons can be fun!! I found when I was younger and in group lessons with 4 other children I got very frusterated as I was ignored a lot since I was more advanced then the other riders in the group, hence why since I was 8 I have always taken private lessons, I like having the one on one connection with the coach and the "attention" I wanted to reach a higher point in my riding. I can completely understand if the child is just in riding for fun or in that "horsey stage" though!!