Hi Keetov--you've just brought up two very good points.
"In a wedge turn (opposing edges), isn't the turn initiated by pressuring the outside ski?" you asked.
The simple answer is "no." But few things in skiing are that simple, eh? It's a "cart/horse" thing, a question of cause and effect. Yes, in a wedge (or parallel--they involve exactly the same movements) turn, the pressure goes to the outside ski. But this pressure transfer is a RESULT of the turn, not the CAUSE. It's the same in a car, isn't it? When you turn the wheels to the right, the car turns right, and the weight goes to the left. But you don't have to tell all the passengers "everyone lean left now so we can turn right"--it's a consequence!
Yes, because the left ski in a wedge turn is pointed to the right, pressing more of your weight on it will make SOME sort of a wedge turn--more of a "zig" than an arc. And, depending on the sidecut of the ski, it will also allow that ski to carve more than the other ski, so there might be a little rounded shape. In addition, usually when people attempt a wedge turn by pressing on the outside ski, they throw in a little upper-body rotation, with further "causes" the turn.
However, while the the movement pattern described in the last paragraph WILL produce some sort of a wedge turn, it does so only by introducing a variety of "dead end movements." It involves what I call "negative movements"--movements in the wrong direction (assuming your intent is to GO in the direction of the turn). Pushing on the outside ski tends to push its tail out, into a skid. Transferring your weight to the outside ski PRIOR TO the turn involves moving your center of mass to the outside.
So the "right" way to do a wedge turn--again assuming that it is intended to be an introduction to the fundamental movements of high-level contemporary turns--is to steer the TIPS IN to the turn. Since the inside tip is in the way of the outside tip, I must steer the INSIDE TIP into the turn first, leading the way for the outside ski. As I do this--as I turn my right tip right, for example--my weight will tend to move toward the left ski. If the turn begins from a straight run down the fall line, the weight transfer will be immediate. If the turn begins from a traverse, or from the end of a previous turn across the hill, the weight transfer will be more gradual. In either case, the weight transfer is mostly a result of the "g-forces" of the turn pulling the skier toward the outside. Since gravity pulls the skier IN to the turn for the first half when the turn begins from an across-the-hill direction, the weight transfer is not necessarily immediate when linking turns.
Your second point is related: "The students don't have enough balance and coordination to release their inside ski edge first."
Remember that in a gliding wedge, the edge is already released! Yes, both skis in a wedge are on their inside edges ("opposing edges"), but a ski does not have to be completely flat to have its edge release. (If it did, we would NEVER have to worry about skidding out of a turn.) It simply has to have its edge angle reduced beyond the "critical edge angle" point. When you stand sideways on a hill, all it takes is a little ankle tension to make your skis hold you there (if you are properly aligned, anyway). Relax your ankles and the skis will release their grip and you will sideslip. They don't need to be completely flat on the snow!
You are right that few beginners have the skills, balance, or trust in their movements to completely flatten their downhill ski, or to lift it up and balance on the uphill ski while "falling" into the turn. This is exactly why we recognize the wedge turn as the first "Milestone" of skill development along PSIA's "Center Line" skiing model. We don't TEACH the wedge turn. We teach these fundamental movements. But more often than not, these rudimentary initial attempts at these same movements of World Cup racers RESULT in a wedge turn!
So a "proper" wedge turn does indeed involve a release of the inside edge--a reduction of its edge angle below the "critical" point--and a guiding of the tips of both skis into the turn. Done this way, it incorporates all of the movements, tactics, and skills of the best turns being done today!