This study uses theory-based design principles to evaluate the effectiveness of an instructional simulation, simSchool. It begins by examining the simulation and evaluation literature, followed by an evaluation of the simSchool software. It is a Web-based simulation designed to emulate various students (reactions) in order to provide practice for pre-service teachers in instructional planning, assessment, and communication. This article uses a framework to analyze the simulation, according to the simulation's instructional goals and design models. The framework for designing a simulation approach to instruction, based on the model-centered instructional theory, provides a detailed model for dissecting the seven functional layers of a simulation. When combined with user testing, results indicated that simSchool provides a valid model of a simulated environment for pre-service teachers to practice instructional activities.