I teach archery to kids once a month for our club. The bows we provide are pretty low-poundage, even for some of the kids. At first, I would stress getting the bow all the way back to full draw, as that seems to be the usual problem with us. However some of the kids would take this to heart and draw the bow all the way back behind their ears! When they overdraw to extreme, it is easy to see why the arrows fly left, because the arrow shaft ends up alongside their head, way to the right of their eyes. Now when I teach them, I stress drawing back to an anchor, neither underdrawing nor overdrawing the bow, because they are just as likely to do one as the other.
Based on watching the kids, I would say that the important thing is to get to full draw, but not draw so much that the arrow moves away from under your eye. Your draw should be "J" shaped. You will be drawing the arrow straight back to a certain point, and at that point, you will have a choice. You can either continue to haul back on the arrow, which will throw everything out of alignment and the nock will end up behind your ear someplace (if you can pull it back that far). Or, you can complete the "J", such that the arrow doesn't move back much further, but your elbow moves around the bottom of the "J" in an arc around your spine, which you should feel in your string-side shoulder blade as that shoulder blade moves in toward your spine.