THis is because parents will ask and you must be able to back up your self up with specific facts.
Next thing would be to contact parents and explain to parents that little Johnny is disrupting class. Have those specific behaviors on specific dates in front of you to back it up. Let the parent know what your grading scale is, placing emphisis on positive participation. Be sure to tell the parent that the student gets a failing participation grade on the days they act out and a passing grade on the days they don't.
Be sure you have established expected behaviors in the classroom. Have your rules posted and go over them regularly. If you have to stop academics to go over rules then so be it. Be sure to document that you had to stop and who was doing the most disrupting. Don't forget to include the fact that you will be contacting parents.
Be sure to make contact with all of your parents early in the school year. Let the initial contact be just a hello I am your child's teacher. If you can, include some positive thing about the student.
I have always found it akward when my first contact with a parent is over a negative situation with their child. It is important to establish a relationship with your parents. Its scary to a new teacher but I have found parents are my best ally.
Inform your administrator what is going on and the steps you are taking. Seek support from other teachers. There must be administrative support. If a child needs to be suspended then a slap on the wrist will just make things more difficult for you. THe kids will laugh at you when you state you will be seeking administrative intervention.
Follow steps set down by your school for misbehavior.
You must be consistant in the application of the system you develop. You can't let something go one day and then come down hard on the student the next.
You can not be their friend or one of them. I don't know your age or how long you have been teaching, but this is a common mistake made by most teachers. Including me! Most new teachers are just out of college and use to being one of the kids. All of a sudden they are one of "them." New teachers sometimes want the students to know they are "cool."
There is an old teacher adage, "Don't smile until Christmas." Kids will run all over you at every chance.
It may take time and it may not happen with this class of students, but once you start contacting those parents on a regular basis the situation will eventually settle down. But be consistant, when you say you are going to do something, follow through and do it. DOCUMENT, DOCUMENT, DOCUMENT>