This paper introduces the design of an agent-based leadership support system exploiting a computational model for development of individuals or groups. It is to be used, for example, as a basis for systems to support a group leader in the development of individual group members or a group as a whole. Using a computational model for Situational Leadership Theory and model-based reasoning techniques, the system monitors and analyzes the development level over time and provides support to the group leader by proposing for different points in time the most effective leadership behavior according to Situational Leadership Theory. The support model has been formally designed and, within a dedicated software environment, simulation experiments have been performed.