How can education change to meet the demands of effectively educating an increasingly diverse student population with the skills, knowledge, and abilities they need to be productive and successful citizens in the 21st century? One possible solution is to create classrooms, teachers, and schools that embrace the progressive and inclusive practices espoused by Universal Design for Learning (UDL). In addition to being rooted in UDL pedagogy, classrooms designed to meet the challenge of 21st century education need to substantially integrate and utilize advances in technology. The vanguard of literature to date in UDL could be characterized as rhetorical advocacy. That is, UDL literature is in the early stages of introducing and promoting UDL pedagogy, but to date there is not a research base strong enough to establish UDL as a scientifically validated intervention (Edyburn, 2010). UDL might sound like a good idea, but until the research base turns the corner from advocating to assessing and measuring UDL outcomes, the promise of this approach will not be realized. This article describes a study exploring effects and outcomes of a professional development program on the perceptions and practice of UDL principles in K--12 public school inclusive classrooms, and could be one step toward bridging the gap from a good idea to a solidified best practice. Specifically, this study investigated a professional development program's effect on teachers' perceptions, conceptualizations, and implementation of UDL principles and practice in their classrooms.