He could be bored, he could be naughty, he could be going through a phase. You dont say how old he is. He could have ADD, my daughter has recently been diagnosed at 15yrs old. She is very intelligent but has concentration problems,and is rather badly organised. If your problem continues it might be worth checking with an Educational Pscycologist. My daughter's work is usually very good but she usually forgets to hand it in,or leaves it at home.
Teachers are usually quite good at spotting dyslexia though but social skills are a bit tricky-you can't force people to be friends.
If there are no real problems, maybe a different school may suit him better.