group dynamics

It wasn't easy to do group work as a kid and I can tell you that it aint easy to do it as an adult either.

Top obstacles
Scheduling - everybody have their days and nights filled with something and it's difficult to find a suitable time for meetings.
Distribution of work - somebody is always doing more work than another. If the distribution of work doesn't even out - it starts to annoy the group members and disturbs group dynamics.
Learning objectives and expectations  -   might be completely different. Some want to do astonishing work, others just want to pass.
Working with strangers. You have to start from scratch. The work can be based on developing friendships, exchange of ideas or arguments. All these are part of group work, but there should not be too many arguments.

Solutions
Regular meetings where group members talk to each other is essential - it is a lot harder to use bad tongue spoken than written.   
It takes a lot of flexibility from all group members to get things done.
Respect of other group members is essential. The time they make available for the joint work, their contribution and input to the work and in best case scenarios the friendships makes group work a great learning experience and enjoyable as a bonus.