Skiing is turning. To turn you must do what? Change edges!
The watershed moment in a skier's progress is when you can change edges at the same time so the skis remain parallel through the transition. That's without any wedging of either ski. It takes patience, timing, and commitment.
I would argue that achieving this is why 97% of students other than beginners come to ski school. If I'm right about that, what strategies and tactics do you deploy as instructors to help them achieve their goal?