My son became 'naughty' and actually it was because he was frustrated and angry as he was having issues. Worth asking yourself is there anythng that could be making him anxıous-big changes in lifestyle new home relatives school-not all kids adjust easily-if a child has changed something has happened-hard for them to communicate it very well. one on one time trying to chat often before they go to sleep children seem to open up- good luck xxxxx
Well, in a way, the teacher is correct. Kids need to learn how to deal with anger. He has learned from other kids. You need to show him better ways to deal with anger. I would look into buying "Cool down and work through anger" or "When I feel angry". This is part of a series of books aimed at 4 to 7 year old's and meant to be read to them at night (several times) and then practiced. Kids do need to be taught how to deal with anger. You do not try and use these techniques while he is yelling. But once he stops or later on in the day - you can refer back to them or pull the books back out.
You can find them here - http://www.amazon.com/Cool-Through-Anger-Learning-Along/dp/1575423464/ref=pd_sim_b_5
Also, Words are not for hurting is another good book. http://www.amazon.com/Words-Hurting-Ages-Best-Behavior/dp/1575421569/ref=sr_1_1?s=books&ie=UTF8&qid=1440993348&sr=1-1&keywords=words+are+not+for+hurting
Finally, just for you, you might want to take a look at - "SOS Help for Parents," by Lynn Clark. Its a very good effective way to change a child's behavior. Hope this helps.