with joy in his heart for learning says a lot for you abilities as a teacher-even if it doesn't count on a test. We often get the stars in our crown when we reach the pearly gates.
He may have long term memory storage problems and I am not sure how they test for that (think Fifty-First Dates). I had the same problems with my Alzheimer's patients. Every day is a new day for them. I would meet them where they were and just roll with the flow. You might want to do a bit of research on the subject and see if there is a strategy you could use.
This is the fallacy of teaching and testing. We can't pick and choose who we teach in public school, and not everyone is/should be college bound.
While I am glad my daughter got her degree, I am happier than she is a kind and decent human being. She uses her talents to problem solve and she has a musical gift to boot.
This little boy could be a PR person, diplomat, or any number of things yet undiscovered. But the most important thing of all, he is a decent human being and you are doing him no harm.