How to evaluate
At all levels look for the three natural moves that you will replace with Ski MovesTM.
1- You can tell a lot about a persons stance with how they stand and walk. Then when you do the static exercise for athletic stance, which happens before every lesson, some students will have major problems coordinating the flexing of their ankles, knees, and hips. Often they will have way more knee flex than ankle flex and have their chest too far forward. If they can not do it on the level, it will not improve on a slope. See the exercises for athletic stance here.
2- When skiing, moving back will be most common followed by rotation and banking. Look to see if they are back at the ankles, knees, waist or all three. Some struggle to get into an athletic stance on the flat, but even if they get it, they will move back when they get onto a slope.
3- For beginners, going too slow, turning too far, rushing from one turn to the next, or starting in a traverse and doing the top part of the turn first will increase rotation and banking. If they start in an athletic stance using a gliding wedge with speed, they will often move back when their focus shifts to making their first turn.
4- For higher level skiers look to see where their body is moving relative to the feet when edging the skis. It should be progressively moving forward and toward the next turn. It is easier to see when viewing from the side as they ski past. Watch for the the knees bending too soon, too fast, or too much relative to the ankles.
5- Look for a problem with symmetry, usually right handed skiers turn better to the left, or they may be worse because they add more rotation using their dominant side. Do they vary how they make turns in the same direction one time better than the next?
6- Can they add variety, are their small turns better than their large turns? Can they skid and carve, ski slow and fast, steeper slopes, different snow conditions, moguls, or park?
There are a couple other moves to look out for: heel pushers, hip dumpers
It can take a long time to replace natural moves with skiing moves, and it is a constant challenge to maintain ski moves. Skiers often regress after improving until ski moves are applied for a longer time.