Developed first in the late 1990s by the Centre for Applied Special Technology, the pedagogical framework known as "Universal Design for Learning" (UDL) has drawn increasing investment from K-12 and post-secondary institutions. The promoters of UDL often frame the approach as being "based in neuroscience," and further as an "evidence-based approach" to instructional design in teaching and learning. While the rhetoric is promising, no rigorous published research has demonstrated any improvement in an education intervention designed with UDL principles in mind. Furthermore, the community of practice around UDL appears to be hostile to questions around the rigor of analysis used to promote UDL interventions. Studies of UDL approaches do not follow best practices in terms of research design, and often solicit anecdotes rather than testing the effectiveness of the approach. The purpose of this policy research note is to survey the state of the art in researching UDL and to clarify the origin of the pedagogical theory. Because the effectiveness of this theory has not been proven, there are no grounds for UDL implementation plans to be framed as "evidence-based" decisions. Further, the reluctance of UDL advocates to rigorously study the effectiveness of their intervention raises important questions about their confidence in the theory. For these reasons, the only evidence-based conclusion that can be made about UDL is that further study is required, as its core claims remain unproven. Institutions of any educational level should proceed with caution before devoting significant resources to implementation of UDL.