Approached the person and explained they had to pull their weight or they would not share in the grade.
Approach the offending party with specific examples of what they are doing wrong and what they can do specifically to fix the problem. Show them -how- they aren't pulling their weight, rather than just saying it. Ask the group member's input on the matter and help them come up with solutions to correct the problem. Anyone can identify an issue. It's the ones that can fix the issue that truly count.
I believe that people need to embrace a goal and believe that they are capable of achieving it in order to be motivated to pursue that goal. I work with my team to develop goals that deliver on business targets and are achievable. By providing the vision, a measurable target, and supporting them with the right tools and information, I motivate my teams.