Recently I've come to the idea that the question "how do you differentiate?" is the wrong question to ask (or at least coming in the wrong sequence). The essential question should be "what do you differentiate?" By differentiating instruction I am changing something for some group of students. To do this I have to ask myself "what can I change and what do I need to keep the same?" What follows are three cases of differentiation, all of which change a different facet of learning.