None of the students learn anything unless everyone's behavior is appropriate. Behavior management is too often played down in favor of instructional methods and grading methods and gimmicks. It took two frustrating years and Fred Jones to convince me of the startling truth. Discipline comes first. Teaching comes second.
Popular theory varies widely about what to do when students are deliberately difficult.
Not all theories assume it is important to know why students are difficult. Ignoring difficult behavior is called 'extinction' by psychologists. The theory is that if the student does not get attention from his antics, then he will stop misbehaving. If the teacher can get all the other students to ignore deliberately difficult behavior, then extinction might work. Our first grade teacher walked around with a yardstick in her hand.