Your son may be bored and he also may have some learning problems. Educators tend to blame kids for being bored, as opposed to figuring out how to stimulate their interests in academics. Rather than speculate about ADHD, learning difficulties, or boredom as the causes for your son's poor performance in school, he needs to have a comprehensive evaluation. Given the teacher's concerns, he certainly would be eligible for a CORE evaluation to determine what the issues are regarding his academic problems. Such evaluations are a student's right, as guaranteed by the law. You certainly could get a baseline evaluation about your son's fundamental knowledge in his academic subjects by having him see a talented tutor a few times. One-on-one time with a creative tutor often yields answers to a child's ongoing academic difficulties. Please engage the school authorities in evaluating your son appropriately.
A child therapist might also come up with some vital information after just a couple of sessions with your son -- sessions where he feels he has a comfortable forum in which to have his ideas and opinions respected. Please don't just medicate him without first exploring the reasons for his academic problems.