That's why the Scoreboard Game is such a lovely part of WBT... use it along with introducing class-yes, and that way you can begin to reinforce what you are looking for... frownie/teacher points for the major standout negatives, and smiley/student points for the positive stuff that you see. Remember the vital +3, -3 rule with the Scoreboard Game so they never get too far behind or too far ahead.
You may have one or two who want to be the 'clown' at first...and that's ok. Respond evenly, with humor if you can, and don't let it get personal. It's not personal for them, so don't let it get personal for you... keep Scoreboard a game, keep your humor and your smiles up, and you will ultimately have the upper-hand, as well as a happier class and a happier you!