The student group possibilistic uncertainty in the van Hiele process of geometric reasoning is considered as the student group capacity for obtaining geometric information. Hence, the student group capacity for obtaining geometric information can be measured by the total possibilistic uncertainty T(r) of an ordered possibility distribution. The capacities of three student groups are found by calculating the total possibilistic uncertainties of these groups. These capacity values set an expectation of future group performance. Future research indications of how the total possibilistic uncertainty may be applied to other models of learning and development will help to establish it as a viable measure in educational psychology.