The best way to handle defiant students is to recognize possible defiant behaviors ahead of time and prevent situations in which students can act defiantly in class. Based on your experience with and knowledge of the class, identify potentially defiant students and prevent putting them in situations that are likely to cause defiance. Work with them one on one, away from other students.
If students begin to act defiantly, keep your cool and talk to them in a polite, respectful tone. Phrase things in the form of questions instead of demands, and model appropriate, respectful behavior. Do not try to force or coerce them into doing something, and never try to physically coerce any student.
If talking to the defiant student politely and respectfully doesn't work, give her a list of choices that are acceptable to you. This allows her to feel as if she has a degree of control over the situation while still behaving within your parameters.
If students continue to act defiantly, write a checklist of appropriate behaviors and have him use it throughout the day to self-monitor his behavior. This allows him to feel in control while allowing you to monitor his behavior.
If negative behaviors continue, speak with the student and explain the positive consequences that will result from good behavior and the negative consequences that will result from defiant behavior, and tell him to choose his consequence. For example, tell him, "If you complete your assignment, you will be able to go to recess. If you do not, you have to stay in at recess and finish it. Which do you choose?"
If the above strategies do not produce the desired results, send a note home or call the parents to schedule a meeting to discuss the student's behavior. You, the parents, and the student can develop a plan for changing his behavior both at school and at home, if necessary.