Psychologists tell us that a student learns only when a task is a little too hard for that student. When a student can do work with little effort, and virtually independently, that student is not learning, but rather rehearsing the known. When a student finds a task beyond his or her reach, frustration, not learning, is the result. Only when a task is a bit beyond the student's comfort level, and the student finds a support system to bridge the gap, does learning occur. This optimum degree of difficulty for learning is referred to as a student's zone of proximal development (ZPD).

Professor of educational leadership, foundations and policy at the University of Virginia's Curry School of Education, Carol Ann Tomlinson has dedicated her career to researching, writing, and sharing about differentiated learning and instruction.

This section includes case studies by Carol Ann Tomlinson and other prominent members of the differentiated instruction field.