Hmmnnn.....I teach 9th grade, and my classes are twice as large as yours, but....well, some classes WILL be more hesitant than others, regardless of class size. All I can say is, don't give up. Remember, it takes practice to be good at something. I started WBT last September on the first day of school much the way you did - Class/Yes, Rules & ScoreBoard. I found if I wasn't afraid to be a bit silly (try LOTS of variations of the Class/Yes and you SHOULD get at least a FEW smiles!) then more of my kids were willing to be silly along with me - yes, even in 9th grade. And, the more fun YOU have, the more contagious it will be for the kids. (And the more relaxed you will get using WBT).
All I can think is that maybe you were feeling a bit nervous and uncertain about trying something new and perhaps the kids picked up on it? If so, just go in strong tomorrow. Maybe start with a Rules Review (using silly voices to lighten things up) and try using the ScoreBoard more - maybe PingPong back and forth to get the energy and motivation level up. In the beginning of the year, I frequently would have 10 or more marks up on my ScoreBoard. And REALLY hold them accountable. If you ask them to mirror your gestures, and they are lackluster, or several kids don't even try, then give them a mark on the More Homework side without even blinking and ask them to do it again until they do it the way YOU want them to. (And if you get to the +3 More Homework side, look for the SLIGHTEST improvement to give them a positive mark).
If they're STILL resisting your leadership, why not involve them in brainstorming for what WOULD motivate them (you could give them a list to choose from if you think that would be easier). I did this further into the year when I needed to "freshen" things up and my kids RELISHED the chance to "vote" for the ScoreBoard weekly reward. (No, I didn't start out weekly - I started out daily....)
Finally, even though it seemed like ALL your students were hesitant, I'm sure some were more willing to participate than others. Look for those small successes and reward them on the ScoreBoard, and perhaps some of your fence-sitters will become go-alongs. (See pages46-49 in the ebook Power Teaching Challenging Teens).
I'm sure others more experienced than I will chime in with their advice as well. Good luck, and let us know how tomorrow goes...
- Jen