If you or your child exhibit the symptoms of ADHD, I highly encourage your speak to your doctor. Your child might be able to tell you when their tummy hurts, or when they’re tired, but they might not be able to articulate that they are not retaining information learned at school, why they don’t remember simple tasks, or why they act impulsively and get in trouble – when you ask them why they did something and they say “I don’t know,” it may be an honest answer.
Mayo Clinic page on ADHD – Contains an overview, symptoms, and more
CHADD – A non profit organization focusing on the study of ADHD and betterment of ADHD individuals