The Comprehensive Application of Behavior Analysis to Schooling or CABAS[R] model is characterized by an organizational system of teacher training and mentoring by those with more expertise in the science of behavior analytic teaching. At the center of the system are the students, whose data drive the system. Decades of research support the CABAS[R] model as a whole as well as its components, which include a fundamental unit of measure and analysis, a criterion-referenced assessment that is also a curriculum, and the incorporation of teacher training modules created to develop teachers who are strategic scientists of pedagogy. When the CABAS[R] system was first analyzed in 1989, data across one school year reflected the increased effectiveness of instruction as measured by student outcomes. Twenty years later, we provide a comparative analysis of data from a similar school where the CABAS[R] model has been faithfully implemented for over two decades. Our data reflect an evolution of the CABAS[R] model, as a function of increased teacher expertise, more accurate and valid measurement and analyses of relevant data, and more effective assessment and teaching strategies, all of which have lead to improved student outcomes. (Contains 1 table and 3 figures.)