At risk of shifting this thread to a topic where the horse has definitely been beaten on this site...
I totally agree with Adbono... I was a HS coach for many years and one of my sons is a college coach. We both have experienced the same phenomena on this from youth through varsity HS and well into college. If your teach is a "slightly up" swing and/or "on plane with the pitch" swing, 99 times out of 100, you get a swing that is more up than the plane. If you use teaches like "level" or "level thru the ball" (as much as many "hitting gurus" will say that is wrong), the hitter's eye will automatically track the ball and lift the swing plane slightly from level to on-plane. The result is also much more likely to produce the desired backspin.
Once a hitter reaches a certain level of competence, understanding and feel for his swing, it's OK to explain what is happening with the eyes and the brain. Good video capabilities can make a difference but even then, many hitters tend to see what they want to see instead of what is actually happening and when.
I also agree with him about teaching lifting the ball at the youth level. It is even more important not to teach lift to a player who doesn't have the strength to get the ball over the top of the defense. If you do so, you screw him twice... building a fly-out swing and not swinging on plane, thus less consistent contact and more swing-and-miss. A hard line drive approach is far more likely to be successful. No one is saying "try for ground balls" (although, when considering typical youth field conditions and player ability levels, that wouldn't be as totally wrong as most claim).
Yes, there are advanced power hitters who, rightfully, have a lift approach. But those players typically have more awareness of their swing, are stronger, see pitches really well and have better timing than most. If a player reaches a certain level of strength and the other mechanic and timing elements are there, it is not a big adjustment to slightly raise the swing plane at that point - not before.
Lord knows there are different camps on this and more than one way to skin a cat. This is the practical application I have found works best for hitters I have worked with.
And, yes, Bob, high tee in a full cage is great for a few different things. Not so sure about the low hands though... I know... see Ted...
Well done Pete! Couldn’t have said it better myself and you are far more patient than I am,