At the core of the PBL process is the group. PBL engages students to work collaboratively and produce a final product. This requires effective groups. If the group isn’t effect then the product produced will not be up to standard or might not be submitted. Too many times projects has have not worked because of group dynamics.
Students within the group need to feel that everyone in the group is contributing to the project. If they are not, effective group management should have embedded group contracts.