Has he had a thorough vision exam? Particularly one where each eye is screened separately. DS has perfectly fine vision in one eye, but the other has huge astigmatism that led to amblyopia and threw off hand eye stuff and close up work. And we didn't notice except for a sharp pediatrician who didn't accept his assistant's assessment that DS just wasn't cooperative. I think you have to eliminate vision before anythng else.
Next it could be they are teaching inventive spelling at K and that is throwing a monkey wrench into everything he thought he understood. Which could make for a pretty stressful mental self concept.
Or he could also be trying to dumb down to fit in with kids.
