I participated in a task during a Precision Skiing clinic last year at Vail. I believe the clinician was Jennifer Simpson. Anyway the task was to initiate one set of turns, like all the right hand turns, using extension and all the left turns using flexion. Then switch sets. Aside from feeling the differences, it’s a useful exercise to deepen awareness of pressure magnitude management.
A few years back I started asking instructors if they started their turns with an up or a down motion. The question gets them thinking about it. Neither is right or wrong unless you consider the application of one or the other at inappropriate times (conditions or turn phases). A good skier, however, will adjust to either end of the spectrum as appropriate without even thinking about it. Or, a good skier will be able to execute one, the other, or combination at will. If you have a student that can’t execute one or the other, well then you have something fundamental you and they can play with in your quest for excellence. 😉