Student success in large enrollment undergraduate science courses which utilize "active learning" and Learning Assistant (LA) support is a complex phenomenon. It is often ill-defined, is likely impacted by many factors, and regularly interacts with a variety of treatments or interventions. Defining, measuring, and modeling student success as a factor of multiple inputs is the focus of our work. Because this endeavor is complex and multifaceted, there is a need for strong theoretical framing. Without such explicit framing, we argue that our findings would be uninterpretable. In this paper we describe our efforts to define that theoretical framework, present the framework, and describe how it defines our methodological approach, analyses, and future work.