FWIW, I’ve heard multiple stories from friends and family about middle school boys not living up to their potential. Often, it’s due to them just not turning in homework (even when they completed it!). Middle school is a tough time for both boys and girls, but I haven’t heard many stories of girls being as spacey as boys in MS.
I wouldn’t worry about him right now as long as he’s got a good attitude and puts in enough effort to put him on the honors track in high school. It sounds like he’s a bright kid.