Universal Design for Learning (UDL) is a framework “to improve and optimize teaching and learning for all people based on scientific insights into how humans learn.” The key is to provide access for all at the start of the teaching and learning process. A great visual for this is the difference between buildings that were designed for the ambulatory, later retrofitted for access (left building with added ramp), and buildings that were designed with access for all in mind (the Guggenheim Museum on the right with its infamous spiral walkway.) Apply that thinking to instruction and curriculum and you have the concept of UDL!
UDL is based on three tenets: