I suspected this was probably the case, but then, the pot doesn't necessarily have to be made on a potter's wheel. There are pre-wheel methods for making pottery, but they're mostly pretty slow, so I would probably experiment with the method of jumping up and down on a fifty pound mass of clay to create a depression, and shaping the clay around that by hand.
I suspect that if that grading procedure were applied in real life, you'd get some wags like me for whom willful perversity would trump efficiency, who would insist on making a single pot even if it turned out to be more difficult than making a handful of really heavy ones, and also a bunch of procrastinators who made all their pots in a rush at the last minute and thus failed to benefit much from practice, turning out a bunch of crappy pots.
If the professor wanted to encourage students to get the benefits of practice, they'd probably get better results asking the students to bring in a new pot every class.
http://www.codinghorror.com/blog/2008/08/quantity-always-trumps-quality.html
For some reason it just seems we in particular could learn something from this anecdote.
Iterate more. The practice effect is your friend as is mining out positive outliers in really huge sets. I wanted to also mention something about using going meta as a way to procrastinate but I feared I would summon a Newsome.
Edit: This has been mentioned before. I think it is good to remind people of it. Desrtopa writes:
It is therefore best to assume this is a parable.