So I have very low level high school students, and speaking is definitely their weakest ability.
Luckily however, I work the the Korean Baduk High School, which means they're obsessed with games, and the crazier the rules, the better.
A clear adaptation of the drinking game; King's Cup, or Circle of Death, or whatever you were peer pressured in to playing when you were younger, this obviously has very different rules. Instead of drinking from the cup, they must take a tongue twister. All the other cards have English speaking related rules and penalties.
All my students, even the quiet ones, were screaming in English, and falling out of their chairs laughing.
Attached is the powerpoint explaining the game - try to demo every card. I.e. For the 8 card, have a staring contest with a student. Practice Thumb Master with the whole class, etc.
Cut up the tongue twisters to put in the cup, and print out a few rule sheets to put out on the table that they can refer to until they get the hang of it. They seemed to grasp the rules pretty damn quickly.
I spilt the class into 2 groups, so about 8 - 10 per group, and give them a pack of cards each. The words on the board can be anything you've been studying recently, plus a few few funny and random ones thrown in there for giggles. Try to put sentence examples on the board to help the lower level kids.
Go forth and educate with controlled mayhem.