This is something that I've run many times before with +Paul Harper during outreach events and I've blogged about it here and +Dana Ernst ran something similar and blogged about it here (both those posts also talk about 2/3rds of the average games).
The way I do this is to split the class in to 4 teams and play a round robin of a set of 5 to 8 repetitions of the Prisoner's Dilemma:
The particular version of the game I usually use is given below:
The utilities represent 'years in prison' and over the 3 matches that each team will play (against every other team) the goal is to reduce the total amount of time spent in prison.
This is always good fun and my final year students were no exception (more so that +Paul Harper leant me a sidekick who was allowed to use a Nerf gun when the opposite team defected - more about that here):