Bill you can have parents participate in the lesson while at the same time make sure that they aren't coaching their child. Think of it this way, in my classroom, when I teach some topic the student is trying to focus on what I am saying. If a parent interferes, it might hinder and not help them understand and so they may get frustrated.
That's what I was trying to say, as well.
If I'm coaching a hitter, I definitely encourage the parent to listen and learn. But I don't want them coaching.