The best time to get control of you class is right in the beginning of the year by setting the tone with a list of rules, regulations, guidelines or any other name you want to give it. If presented in a positive way, they will, for the most part, be happy to follow the ground rules you set forth. Have your students sit down in each class, preferably the first one they take and go over each important matter you would like to have in place.
It is also recommended that you give them a print out of the rules to bring home to help the parents understand that it is not a free for all and that you are not just a babysitting service. Some of the topics we like to talk about are: proper grooming and class attire; no gum chewing in class; no talking (this is a big one to get across); the importance of being on time and paying attention; how to respond to correction and not to take offense when one is given; respecting teachers and fellow dancers. I am sure you will come up with your own laundry list of pet peeves when you do this. This is the first step in gaining control of your class and letting them know that there are boundaries. Students do respect them but will try to push beyond them. You can then revert back to the guidelines and remind them that everyone is expected to follow the rules.
Dealing with that one problem child is always a tricky situation and must be dealt with carefully. If a student is reprimanded I always like to follow it up with a smile shortly afterwards so they now it is not personal. Once they start to see that you mean business and that the guidelines are to be followed they will start to get with the program! Sometimes parents will come in and say "you yelled at my child " ! You cannot remember doing so and you probably didn't but the student's perception is that you did. So how you reprimand the student is very important. Try to focus on the behavior not the person. Let them know before the class is over that you do not hold any grudges. we hope! You can achieve this by saying something good about something that they did well during the class, even if it is a stretch!
A business consultant once told me that before you can give someone a correction at work you must first give them 3 good things to hear! It's the 3 to 1 theory, this is pretty hard to do all the time but I have found that when students like you and feel that you think they have something special, they are eager to please you. If you don't have the benefit of starting at the beginning of the year then I would recommend that you teach the first class and make mental notes throughout of things that you don't like or feel that are not conducive to the learning process. Then approach the studio owner and ask if you can set some guidelines to help the students learn faster and have a more pleasurable experience. Then, sit the class down and set the new rules in a fun and upbeat manner. I never like to make it sound like they are going to jail! I have been to studios where things are so out of control I don't know how the teachers can stand it! If you are spending too much class time reprimanding it could be a sign that you are losing them and it would be a wise idea to stop the class and calmly go over the guidelines again and again if necessary. Sometimes the only thing left is to dismiss a child from the class. This is always dramatic and will pull the whole class into focus. I would recommend talking to the one that was asked to leave the class before they leave the building and letting them know that their behavior will not be tolerated and that if it happens again they may not be allowed to take your class anymore. We all know that some classes are great and they always do the right thing. We also know that there are some classes that you just want to pull your hair out, or theirs! But you can get them in order just by setting guideline to keep them in place and keep using them to refocus the group as needed. Good luck!