The idea of a progress variable is not radically new—it has grown out of the traditional approach to test content—most tests have a “blueprint” or plan that assigns items to particular categories, and hence, justifies why certain items are there, and others aren’t.
The concept of a progress variable goes beyond this by looking more deeply into why we use certain assessments when we do (i.e., by linking them to growth through the curriculum), and by calibrating the assessments with empirical information.