Regardless of what his teacher says (or whether his behaviour is the same at home, since environment does make a big difference) definitely take him to the paediatrician, ideally one who specializes in ADHD. You probably have a good chance of getting an accurate assessment but lots of kids (girls, mostly) have ADHD and are diagnosed in adulthood (like me) or not at all, which makes our lives very difficult. The quicker you can get the assessment done, the better. Good luck.