His difficulties with school didn't end when he came home. He couldn't concentrate and homework took him hours. He would stop a million times to go to the refrigerator or bathroom. This inability to deal with the structure of school may interfere with learning and academic achievement.
Symptoms usually start before a child reaches age seven and last for six months or longer.
Seeing signs of ADHD doesn't necessarily mean that a child has the syndrome, so discuss your observations with your pediatrician.