From someone who is reasonably adept with ceramics and just bought another 100 pounds of clay this morning (aka I know how much 50 pounds of clay weighs) because I'm making a six foot tall piece in an intermediate/advanced ceramics class that I'm taking for fun: 50 pounds of clay is actually a lot, and not everyone can make a pot that big. So if someone managed to make one 50 pound pot, it would still require quite a lot of work. Plus, there's the assumption that the majority of the people in the class are interested in learning, so they will be trying to make something good.

It's a story about students with some internal desire to be good at pottery, not just to get good grades. The grading system forces them over the hurdle of hesitation, to produce quantity without being paralyzed by anxieties over not being good enough, and then their own desire to improve nonetheless uses that imposed practice productively.

I think the point was that they didn't do that, even though they could have.

Also "learn from mistakes" is taken for granted with quantity here, but it is very far from reality that learning comes inherently from practice. In the example, I would assume a student graded solely by weight couldnt care less about learning. I would create 10 pots reaching the minimum quality possible to be considered a pot and move on without looking back.

Also, it is very reasonable to assume that a student graded by quality would practice a lot and discard (and learn with) the worst pots.

You clearly know what's wrong with parable, so adjust it accordingly. Give an A to the top 25% of the class when sorted by number of pots made.

If someone told you to produce "a huge quantity of ceramics" would you go for huge in size or huge in number of items made?