Hello,

I'm currently trying to set up a group matrix for a multiplayer game that only consists of a subset of players. 

For context, I have all players complete a quiz before they begin playing my game to ensure they understand the rules, and I only want players who have passed the quiz to be able to play the game. The problem is that when I shuffle my groups after each round I need to do it in a very specific way that requires matrix shuffling, so I can't just gate progression behind getting the quiz questions right because all players have to arrive at the end for the groups to reconfigure. If I can't do this, my only two options are to have everyone else stuck at the waitpage forever or to drag the players who fail the quiz forward but not let them play, resulting in at least one dead group every round. 

Is there a way to boot them out before setting up my initial groups, and then running the game as normal from there?

I have not completely understood the intended design of your study.

Will your participants play a different game in each round? And, thus, will there be a different quiz at the beginning of each round, with subjects who passed the respective quiz participating in the current game?

Or will there be a single quiz at the very beginning, followed by multiple rounds of game play among only those participants who passed the initial quiz?

There will be a single quiz at the very beginning, followed by multiple rounds of game play among only those participants who passed the initial quiz.

Just to be sure, would the following apply?

(1) All participants arrive at (approximately) the same time. That is, you invite all participants to join the experiment, say, at 10 a.m.
(2) You grant everyone a particular amount of time to read and understand the instructions (say, 7 minutes). You also grant everyone a certain amount of time to solve the quiz (say, 3 minutes).
(3) Everyone who has not read the instructions and answered the quiz correctly in time will be excluded.
(4) This way, for those who are allowed to participate, the amount of time that they need to spend on a wait page will be limited (to a maximum of 10 minutes total in my example).

Yes, all of this applies.

Please have a look at the attached code.

It implements what you desire using three apps, one for the instructions plus the quiz, one for the actual game, and one for a feedback page.

My example code assumes a group size of 2. People who fail the quiz skip the game app and are advanced to the feedback page. Also if the number of participants who answer the quiz correctly is odd, one of them skips the game app and is advanced to the feedback page.

Inside the game app, the group matrix is shuffled after every round. When doing so, only participants are taken into account who have answered the quiz correctly.

You're my hero. Thank you!