There is more than one way to solve a problem. The solution must be safe and cost effective with regards to time and effort. The need for a social structure that relies on cooperation must be stressed to the students. The social skills used and practiced are just as, or more important than the thinking skills. Without cooperation, there can be no success.
Group size is critical.
Let the students choose their own groups. Group size should range between 5 and 7 students. The ideal group number is 6 students. Do not offer solutions. The main principal of teaching problem solving is to never offer solutions.