Counterpoint- moving to a wider ski, within reasonable limits (Ie an 85-95 waist ski, not moving from 78mm rentals to something in the 115+ range) teaches somebody the skills needed to effectively edge.
On a skinny ski, it just doesn't take much to apply force to the edge (not enough force to be an effective skier, but enough force to change the direction of travel of the skier). I see many beginner/intermediate skiers do it by rolling over their ankle from side to side and using the play in their generally loose boots to get the ski to grab an edge.
When you put a skier on a fatter plank, they are forced to learn to angulate to engage the edge.
Clicking into fat skis for the very first time is an interesting experience and I am sure a near-universal one. You go through a series of barely controlled or uncontrolled turns before you learn to exaggerate the movements that you used to engage the edge on a skinnier ski. After a day, it becomes second nature.
I went about 4 seasons where my skinniest ski was a 95 waist. When I clicked back into a 72 waist ski after seasons where 95% of my time was spent on a 118 waist ski, I found that I was throwing WAY TOO MUCH angulation into the skinnier ski and getting more turn than I was wanting. Similarly, I also had a day where I went from my 118 waist skis to a pair of 1984 Dynastar Course skis. It was scary, because again I was throwing way too much angulation in, and locking a ski into an unintended super long radius turn. I had to learn to be very cautious with angles so I could skid the ski (or actually make the attempt to bend the very stiff ski enough to make a shorter radius carve- a tall order.
I have a theory that a very good way to teach a low intermediate how to achieve good angulation is to move the intermediate progressively up into wider skis throughout the ski day. Choose wider skis with a healthy sidecut/short radius, and have them ski each ski until they were proficient in engaging the egde before moving wider. Then, move them back to a more appropriate ski (you know, one in the 85-95 range) and let them use their new skills to really throw force into that ski.
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