[mesmark]

I do the same, dividing my classes up into groups of 4. I just use plain printable board games, not snakes and ladders. You may need to model how to play and certainly make sure they understand the speaking tasks.

That means you'd have a lot of groups to walk around and monitor. You may find a few hot and cold pockets where some are really into it and others aren't. It could be the personalities of the students. It could be a close game that makes everyone excited, or if it seems hopeless they may give up. Like eaturchees said, it could have been that they were hungry or just yelled at in the previous class.