A family of models for the evolution of a population of interacting individuals of different social classes is studied. The social state of each agent is represented by the value of a variable representing his wealth. The wealth can only have discrete values and the interactions among the agents are of quadratic type. Under some assumptions, the authors show that the constant distribution (i.e., same number of individuals in each social class) can be an equilibrium of the system. Simulations for some particular cases are also presented. (Reviewed for MathReviews, MathSciNet, 2006).