This is likely a straightforward question -- forgive my ignorance. 

I want to run an online experiment. I want it to work like this -- players go through a consent form and instructions individually. After this, they are pushed to a different app using redirection where subjects arrive at a waiting page. I want the second app (the actual experiment) to start once N players have arrived on the waiting page. Ideally, this will happen every time a group of N players has arrived at this waiting page. 

How can I do this in oTreeStudio when N > 6?

Define group_by_arrival_time_method (subsession function). For example to make groups of 10, do this:

def group_by_arrival_time_method(subsession, waiting_players):
    if len(waiting_players) >= 10:
        return waiting_players[:10]

(Yes you are right oTree Studio's drop-down only allows groups up to 6 people but with the above function you can make it whatever you want.)

Thanks! Works perfectly.

Hi Chris, I also have some troubles with oTree Studio regarding the number of players per group.

I'd like to invite 20 participants to a session and divide them into two groups of 10 players at the beginning of the session. There is no interaction between the two groups throughout a session (i.e., fixed matching). Each group plays an identical game 50 times (50 rounds). 

Despite no interaction between the two groups, I want both groups to move together from one round to the next (i.e., all 20 participants must submit their decision to see the results screen for that round). In this way, both groups end the session at the same time.

I would really appreciate it if you could help me to do these with oTree Studio.

Use wait_for_all_groups = True

Thanks Chris. I understand that wait_for_all_groups = True allows the two groups to proceed to the next round together.

But, first of all, how can I create two groups of 10 participants at the beginning of a session in oTree Studio, which allows group size up to 6 participants?

Same solution described above (group_by_arrival_time_method).