Behavioral models, mathematical models of a systems ability to meet customer needs, are useful evaluation tools throughout the design process of systems. Currently, behavioral modeling is conducted at a component level. The models used to evaluate a system are associated exclusively with the components used to solve a products desired functionality. As a result, it is often difficult to create behavioral models during the early stages of design when these component solutions have not been identified. However, during these early stages of design, information about the desired functionality of the system is known. The objective of the work presented in this paper is to develop a method that uses this information, in the form of functional models, as the basis for creating behavioral models. The paper proposes a five step method for creating the behavioral models from the functional model. Significant contributions from the work include reuse of behavioral model elements based on common functionality, swapping of model elements with varying fidelity, a framework for mathematical concept evaluation and selection and the linking of assumptions made during mathematical modeling to their effects on the functionality of the product and vice-versa. Two examples of the method are included, a summary example of a resistor network and a complete example based on the dynamic modeling of a Formula SAE racecar. Conclusions from the work and examples are presented along with areas of future research.