When I have used group assignments in a problem solving class, I had students give answers the the questions after they had discussed and agreed on the solution. Since in problem solving, the method is more important than the final answer, the focus was on how to go about solving the problem. I encouraged them to give multiple methods of solution, providing they agreed that all methods were viable. They were not asked to evaluate which methods was "best" because that was dependent on how you thought about the problem. One method may be more efficient, but not as evident.