Fair Isn't Always Equal by Rick Wormeli - Differentiation

This book focuses on the idea that differentiated instruction should also include differentiated assessment and grading.
The first section focuses on differientiated instruction, why we should do it, and how it should work. This is mostly review for many of us. However, one of the first points that strikes me is the idea of determining what it means to master a subject/topic/objective. As we have focused more and more on the Standards of Learning we have become proficient at analyzing objectives and considering exactly what it is students need to know. However, I don't think we are as strong at identifying what it means to master something. This takes an even bigger picture view than I am accustomed to.