I would suggest starting with his red flag for future problems. The "smart" label. Young children often perceive smart as "getting all the right answers" and/or "knowing more than my classmates". This is a huge problem because these children are likely to stop participating because of the risk of getting the answer to a question wrong. When they eventually reach a point where they don't "just know" the answers and start getting things wrong, they can have an identity crisis! If the only facet of identity they recognize in a social setting is being "smart", when it doesn't come easily, then "I'm not smart" and that's earthshattering for them.
Your son's play based school might be perfect for him right now. I would suggest asking his teachers to praise his character traits rather than his knowledge. If he can start building his identity as "I am kind" or "I am persistent", he will have more resilience than if the core of his developing identity is "I am smart."
I would suggest looking for mentors for him - perhaps a teenager. Someone who can model their mistakes. It was life-changing for me - in high school as a anxious perfectionist talente artist - to have an opportunity to see a professional artist's sketch pad. I was dumbfounded! There were mistakes. There were sketches he quit and started over. Even the professionals I idolized made mistakes. I had no idea. And even recently, in my 30's, I claimed to hate math. Until I took a math class with a professor who wasn't pompous and confessed his mathematical errors without embarasssment. It was then that I learned that the secret to math isn't a lack of mistakes - it's checking your work to find your mistakes.
Be free and relaxed making mistakes. Admit them to your son, model them, let them be a continuous non-event.
