Stop trying to teach people "Perfect form." There is no such thing!

There is no such thing as perfect form, only good technique. There is no "one size fits all" for exercise and athletics. Seem like semantics? 

I was asked this question from a trainer once:  "If you had a 16 year old baseball player that threw a 90 mph fastball, but his throwing motion looked funny, do you tell him he needs to change the way he throws?"  If you do change his mechanics, how will that affect his velocity? 

I see this at the gym all the time.  People trying to "correct" each others form.  For example, I was resting by the squat rack today and someone was trying to teach someone how to squat.  They were telling them that they need to narrow their stance, and point their toes straight forward, and keep their knees from going over their toes, and to stick their butt backwards, etc.  I don't think it even occurred to these people that they may have a different shaped pelvis, different femur/tibia lengths, different ankle mechanics.  This is exactly why some people can squat comfortably and almost sit their butt on their heels, and why others have trouble getting thighs to parallel. 

When I am teaching/coaching someone exercises, I often give them as few instructions as I possibly can.  For squats, my instructions are usually as simple as; "let me see you squat."  If corrections need to be made to technique, we start by make alterations from there. 

The moral of the story is that everyone does things differently.  We should stop trying to make everyone do things the same way.  We should allow them to work within their limits and try to improve on technique with every session.