Take a deep breath and relax..it's not you it's them. Try a rewards system if you haven not been inducted into the school's system. hand out raffle tickets to kids behaving and say that there will be a draw at the end of the lesson. i have red clicker and green clicker and every time i see good behavior i click the green and the same with the red for badness... I tell them that if at the end of the lesson there are more green than red there will be a treat use the c1 c2 c3 c4 method in your classroom c= consequences if this is well established in the school don't take the behavior personally don't react to minor disturbances unless absolutely necessary concentrate on good behavior I went to a school 3 days last week kids perfect went to one rated 1 ofsted and they were dreadful. Even in a school you are working in you will have this so it's good to try out different behavior strategies while earning money... Keep your chin up.