The two most frequently used specifications in stage-specific family structure analyses of young adult outcomes-state 9 stage and event 9 stage-impose restrictions on the parameters of the underlying model of child development. The restrictions imposed by the state specification have substantive a priori disadvantages, implying that use of the state specification requires justification by a specification test. Because the state and event specifications are non-nested, a classical approach to specification testing runs into practical problems. We demonstrate the advantages of a Bayesian approach to the specification testing problem using two applications to young adult prosocial behavior-charitable giving and volunteering. Substantive results are that family structure transitions during adolescence are negatively associated with subsequent giving, and transitions during middle childhood are positively associated with subsequent volunteering. There are other substantive results that would have been missed had we not realized that the state and event specifications impose restrictions on the underlying model and had we not made specification testing a prerequisite for substantive analysis.