In fact, so I can remember exactly what was said, I'm going to copy/paste the responses here:
1 Good job! Try to keep the circle as even as possible and watch the shape of the jaw.
2 Good job! Watch the shape of the circle and the ellipse that represents the side plane of the head. Make sure that they are as even as possible. These shapes will affect the overall shape of the head and need to be correct from the very beginning. Try to copy Jeff’s examples as closely as possible.
3 Not bad but try to keep the lines as smooth and even as possible. Try to make the circle even and watch the shape of the jaw.
4 Not bad but try to copy Jeff’s example as closely as possible. There are specific measurements and proportions that need to be learned by copying his drawings. Watch the shape of the jaw and make sure the side planes of the head are the correct size and shape.
5 Good job! Watch the shape of the circle and the ellipse that represents the side plane of the head. Make sure that they are as even as possible. These shapes will affect the overall shape of the head and need to be correct from the very beginning. Try to copy Jeff’s examples as closely as possible.
Added the pictures to remind myself which comment was for which drawing. I've printed up the images from the workbook (Jeff's drawings) and will be tracing them in a bit, then drawing freehand to try to get closer.
Followup - I see that the responses saying "Not bad" are from my earliest drawings and "Good job!" from the later ones - I was really clumsy at first and my lines got better as I went.
Just dug up my old folder full of templates and found the circles, used it to draw a few perfect circles on a newsprint sheet and proceeded to fill the rest with my own freehand attempts. Mine started really bad (not warmed up yet for one thing) but I learned a few things from this:
1. It seems I do slightly better counterclockwise than clockwise. Opposite of Jeff. Not sure which way I went though on the ones where I slid my hand (see #3below).
2. When I correct mistakes in the circle I tend to overcompensate - go a little too far in the other direction.
3. Remember to lay my last 2 fingers completely flat against the drawing surface and slide my entire hand smoothly over it - this results in much better circles (well, they're still not really circles, but much smoother now and getting closer).
I'm not sure I'll ever attain Jeff's level of accuracy and precision, but I know the hard striving is important. It's equally important to think your way through problems - much better to come up with a plan of attack rather than just keep butting your head against the same wall endlessly. And if your plan isn't working, modify it. Mid-course corrections are vitally important.