There are a couple of things to consider. First, the heavy end of the board always wants to go down the hill first. Second, a beginner is almost always going to have speed anxiety and lean too far back. Third, in order for torsional twist to be effective, the front half of the board needs to be weighted. Fourth, a beginner has got a lot of new information to process and try to use so keep it simple at first. Fifth, the terrain a beginner should be riding is not so steep that staying in a static, weight forward position, will pose any real problem.
I find that the most effective teaching technique is to have the student keep their front knee more bent than their back and to shift their torso toward the nose. Then use their front ankle to pressure the toe and heel edge of the board to initiate basic skidded turns.
Later on, when a rider starts getting into more intermediate riding tasks, dynamically shifting weight becomes essential and by that time, the student has enough experience to understand more complex riding tasks. On steep, black diamond terrain is is critical to start the turn with an aggressive forward shift of their weight and as they complete their turn, shift that weight toward the tail. This forward aft movement is so key to maintaining good control and edge hold on steep terrain.
Part of the reason the intermediate rider often reaches a plateau in their riding and seems to always struggle in very steep terrain is that they have had the idea of getting forward to initiate turns so ingrained into their minds, that they forget that there is absolutely a time to move aft. Along with correct timing of flexion and extension, good forward-aft movements are key to dynamic riding.
Also, remember the 4 board performance concepts of Twist, Tilt, Pivot and Pressure. To be an effective, efficient rider, we have to use and manage all four with good timing, intensity and duration.....