There are 2 meanings here. Is the teenager troubled meaning upset about something or are they causing trouble in the class by being rude etc?. If they are being rude it is best to start the next class by stating the rules you have for the class and the consequences of breaking them. If the teenager is upset, ask to see him/her after class and ask what is bothering them.

Children will probably be troubled at this age. Make sure they do it intentional or just can't control themselves due to the age. At least, don't let them influence others. Think about yourself, what you were be and thinking at that age. I agree with this point of Marie-Hélène, keeping positive attitude to them and being kind of them.

Hello Safaa The best way to deal with a troubled teenager is to ignore him/her... But you need to keep an eye on him/her and look for a positive attitude and congrate him/her for that ... It is easy to say but not always easy to do...