Your marks are Dependant on the group working together, and coming to a satisfying conclusion as much as it is about doing the task.

How about using compromises? If they don’t wish to talk, they do the main research and summaries of the text or the lecture aids and those who don’t mind talking can then help write up a lecture they are willing to do using the summaries.

you will have to be assertive (not rude and bossy but strong) if you want their respect as a leader…

for a final resort you may have to threaten with outing them to the teacher. If someone is not pulling their wait often teachers do not know unless you tell them, and then they will alter the marks to ensure you get more where the slackers get less.

Cheers

-KM

Tell the group that you are a democratic leader and are willing to hear their ideas.