...aaahh, the curious mind, it's a wonderful thing.
I too, have wondered about this "windmilling prop" during simulated engine failure training.
I now understand why singles are not made with feathering props - too heavy and expensive - but VP props should be pulled to coarse pitch for minimum drag and most forward lift, or "pull".
The training in this technique is just not there in our systematic approach to emergency training. Simulated engine failure in singles is introduced, usually, in fixed-pitch singles, and current philosophy is to not actually kill the engine with mixture so that the prop can be stopped by slowing to near stall speeds. This works and I personally encourage it - safely within gliding range of a runway of course - but most people don't, and that is my point. We don't teach stopping the prop for best glide distance.
However, as my experience tells me now, the problem with most pilot trainees is not getting the maximum distance, but getting rid of excess altitude and airspeed. Most of the training I do on forced landings deals with the student coming in a "little high-and-fast" as it should be on a forced landing, and then, when making the field is assured, proper use of slips and flaps to get the airplane down into the field in that last 3 or 4 hundred feet.