Without any notice, I think that teachers automatically differentiate instruction. It could be that you assign different assignments to students or you allow students to do the same worksheet but grade on the ability. Differentiate is the new buzz word for MPS. It also goes back to the days of the blue jays and the robins. Kids know what ability level they are at compared with their peers. When we separate the work the kids know. The way I handle it in my room is I often pair lower achieving students with higher. Each student is responsible for the work. My kids enjoy working together and teach one another, even the lower ones.