This thesis presents a tool for the mechanical validation of formal software specifications. The tool is based on a novel approach to incremental validation. In this approach, small-scale aspects of a specification are validated, as part of the stepwise refinement of a formal model. The incremental validation technique can be considered a form of "lightweight" model checking. This is in contrast to a "heavyweight" approach, wherein an entire large-scale model is validated en masse. The validation tool is part of a formal modeling and specification language (FMSL), used in software engineering instruction. A lightweight, incremental approach to validation is beneficial in this context. Such an approach can be used to elucidate specification concepts in a step-by-step manner. A heavy-weight approach to model checking is more difficult to use in this way. The FMSL model checker has itself been validated by evaluating portions of a medium-scale specification example. The example has been used in software engineering courses for a number of years, but has heretofore been validated only by human inspection. Evidence for the utility of the validation tool is provided by its performance during the example validation. In particular, use of the tool led to the discovery of a specification flaw that had gone undiscovered by manual validation alone.