A previous research report described a prototype measure of the skill of negotiation in interpersonal competency and the results of an initial validation study of that measure. This report describes the results of two further validation studies of the computer simulation negotiation skill measure. In study 1, 37 second- and third-year law students nearing the end of a course on negotiation participated as experts, while 248 high school students served as novices in negotiation. Results support the construct validity of the measure, clearly distinguishing between experts and novices. In study 2, 51 high school students randomly assigned to groups performed the simulation as teams. As expected, three-person teams performed somewhat better than two-person teams, but there were no significant effects of group size. Results indicate that a collaborative environment is feasible. Both studies also demonstrate that cognitive biases are associated with lower negotiation performance, and that experts exhibit more self-regulation than novices. Appendixes describe the negotiation scenario and provide two study questionnaires. Two figures and 29 tables present study findings. (Contains 38 references.) (SLD)