He was riding in about 10 minutes.
I was amazed. He scooted around without pedals for a few minutes and the teacher said he was ready. The pedals went on and he was off and riding. "This is as easy as eating peas!" he said. Easy peasy, indeed.
After the class we went to a park to practice some more. (And to show off for Gramma and Grampa.) He's got it!