To open up a discussion for all of you youth instructors (4H, School Shooting Sports, etc) let's assume you have had problems with the parents interjecting, which most of us have.  Whether it be organized sports, shooting sports, etc., We as parents have a hard time of letting someone else step in and instruct our children, regardless of their resume.  I have only had it happen a couple of times.  

One was dealing with an 8 year old with a severe flinch, turns out Dad had been "making a man out of his son" (his words, not mine) and teaching him to shoot with a 7mm Rem Mag...alot.  I did all I could do to help that kid, but his father insisted on him knowing how to handle a big game rifle at 8 years old....everytime I made strides in curing the flinch, they would have another range session the next week.  I finally had to give up, and tell him if he wanted a child that was an accurate shooter, he needed to cool it with the belted magnums for a couple of years.  That didn't go over too well, and I pretty much had to give up on the kid because of dad (which I hated to do).

Anyone else had similar experiences?  At what point did you just have to give up?

It happens often.  Parents...usually the father have unrealistic expectations that exceed a childs physical and mental abilities.  Father is trying to do right, making the child achieve.  But, sadly often the child is overwhelmed and stunted in that expectation...since father usually resorts to loud insulting humiliation to vent his frustrations.
I coached a kiddie soccer team.  Most parents, that showed up for practice, would ignore the kids and visit among themselves. BUT, come game time on Saturday, Father was always on the sidelines screaming at his helpless child for not being a super player.  I had to ask one Father to stop hollering, "Whats wrong with you" at his 6 year old son who was trying his best.

All you can do is give reassuring advice, training, encouragement and hope the child is able to remember  some of it.
All you can do is try.