When I have a difficult class, I'm willing to try almost anything to maintain a productive atmosphere. ClassDojo is one of the things I tried, and it has worked pretty well with my kids.
Once you sign up, you'll create your classes. Since I have two classes, I titled them "homeroom" and "switch class". I know, super creative. In each class, you'll have to input your kids' names. Dojo (as me and my students call it) will randomly assign avatars to each child.
After I put in my students, I changed the positive and negative behaviors to those that work for me.
I don't use it every day because I don't want my kids to get bored with it. I like to change things up to keep it fresh sometimes. When I do use it, I'll either project it on the SmartBoard or on my TV. Apparently you can also use this on your phone while walking around the room and in the halls, but I haven't tried it.
To make it worth their while, the person with the most positives at the end of the day (or sometimes end of the week) will get some kind of reward like a homework pass or a pencil. Students who end up with 3 negatives at the end of the day get a "mark" on their Responsibility Card.
The kids enjoy it, and it provides a little incentive/reminder to stay on task.