It would be a better idea if you found out if he was upset by anything in his life at home or at school,before you took the route of ADD a lot of children round his age do not take responsibilty seriously does he seem happy with his school and teachers have you talked to him about anything upsetting him, have their been other changes in his life.
He seems generally happy, Except when he is compared with his brother who is doing extremely good in studies and music. he plays sports and he loves sports
Be a good idea not to compare especially in front of him, probably wont build his self esteem to hear his brother praised a lot whilst he is struggling, focus on his positive side , does he do sports and outside activities are you involved in games with him, does he get plenty of positive attention.
I have just responded to your post at the top also