Not really counterintuitive. This is the struggle many heritage speakers have, regardless of the language. As with any language, kids learn to understand and speak it long before they learn to read and write it.
LOL I can see his essay now - “Spanish is my hardest class. And yes, I speak Spanish with near native fluency”
I will post when I have more information. But if it doesn’t affect him to lower to SL even though he will be entering his senior year I may just let it fall where they may.