Apparently the "ceramics class" story that you see all over the place after it appeared in the book "Art and Fear" was a modification of this real story, retold in a closer-to-original form in "Atomic Habits."

The Art and Fear authors credit Uelsmann himself as the source of the story; whether I believe he really did it with actual students for a whole semester, on the other hand...

It's a little bit of a "just so" story in any form, though the lesson of repetition is fine regardless of its literal truth.