Your instructor is misinformed. They will not make a horse travel in frame. They may help when used briefly along with a LOT of leg to PUSH a horse into frame.
I am afraid a lot of people drag a horse's head back into a vertical face 'head-set' and they think they are teaching the horse to travel 'in frame' and 'collected'. You cannot drag a horse into frame from its head back. You MUST push a horse's hind end forward and use skillful hands to elevate the shoulders and keep a horse's head in an acceptable position. Then and only then do you have a horse framed up and collected. The hand forms a barrier, they do not pull the face back.
Draw reins, used briefly, may help get a heavy and very resistant horse learn to respect your reins and hands a little better, but they really are a crutch that usually ends up just dragging a horse's nose back and allowing (or encouraging) it to travel heavy on its front end. They end up accomplishing exactly the opposite of what people are trying to get done.