Sometimes we have project groups work on an activity in class,
where we can observe them and make suggestions about procedure
and group dynamics.

Occasionally a student expresses the wish to work alone on the
projects. Usually, we assign such a student to a group for the
first project but permit her or him to work independently on at
least one subsequent project.

Second, include a project-related question on the next quiz or
exam.

Finally, you can adjust the group membership for subsequent
projects. A method that we have found effective is to put the
non-workers together in a group. This solution is not intended
to be strictly punitive---often such students were simply quiet
or intimidated by other group members. Putting such students
together in a team often draws them out. This makes the other
students feel better and often has the happy result that the
members of this new group become motivated to do a good job on
the next project.

A related question, of course, is how one identifies students who
are not carrying their fair share of the load. One method we
have found effective is to require students to submit
confidential peer evaluations of all other team members at the
end of each project.