One of the most trying parts of being a teacher is dealing with the unruly students who are constantly disturbing the other students who want to learn. There are a few tactics you can use to control the disciplinary-challenged kids in your class.
Move them to the front of the class. It is harder to disrupt when everyone is seated behind you. The disruptive student does have the vantage point of watching, commenting and distracting the other students that sitting in the back of the class allows them to have. Also, disruptive students are usually incredibly insecure. Sitting in the front row of class plays on their insecurity; they believe everyone is looking at them and not because they are the class clown, but because they're exposed at the head of class.
Engage them. A lot of students that are disruptive lack attention span. They are easily bored. So try engaging them. Get to know them and find out what interests them. Use their interests to try to bring them into the discussion. Once they're actively engaged, their interest shifts from class clown to interested pupil.
Ask them nicely. Most kids respond to being put in a leadership position. And disruptive kids enjoy being followed. So pull them aside and ask them for their help. Let them know how much the other students look up to them and ask them if they would be so kind as to assist you in making the entire class pay attention. You'll be surprised what assigning that kind of responsibility will inspire in a kid who probably feels out of place.