It sounds like he’s developing a negative attitude and self-image due to untreated ADHD. He’s seeing that he cannot perform like his peers and, absent of another explanation, he’s assuming that he just can’t measure up. I would pursue an evaluation and diagnosis so he can get treatment. It can make a monumental difference.
Here’s everything you need to know for that process:
And the information you need to consider treatment:
ADDitude Community Moderator, Author & Mentor on Parenting ADHD, Mom to teen w/ ADHD, LDs, and autism