The study investigated the predictive ability of two sociological theories of group decision making, the social decision scheme (SDS) and the valence distribution (DV) model. The theories were applied to a normal classroom setting of grade-9 and -10 students (N = 159) involved in a scientific inquiry—a simulation of scientific decision making. In their attempt to resolve conceptual conflicts concerning a pendulum's period, the students worked towards a consensus. It was discovered that student beliefs at the end of the simulation deviated from this group consensus. Neither the SDS or the DV theories could account for this result, except in one extreme case. The psychological state of the decision makers (vigilant, hypervigilant, etc.) was mildly associated with this deviation. The predictive function of the SDS and DV models was apparently severely hampered by the natural complexities common to classroom interactions. However, the study did illuminate factors that likely affect conceptual change in the context of classroom group decision making; and the study discovered strategies which students invented in order to maintain their alternative conceptions of motion related to the pendulum, in the face of conflicting evidence. These results are discussed in terms of the students' participation in the scientific inquiry.