You might hear or read about “differentiating instruction.” This refers to the process of adjusting lessons to best meet students’ needs. In the CPM program instruction is differentiated by the way students approach problems. Theorist Jerome Bruner states that the ideal progression of activities for learners is to go through the enactive stage (this would be using concrete materials -- integer tiles, algebra tiles, models including computer-generated ones, etc.), then the iconic stage, in which students draw pictures or use mental imagery developed from their experience with the concrete materials, and then move to the use of symbols to represent the concrete. In a CPM classroom students are allowed to move on to the iconic and then the symbolic stage when they are ready, while the physical models remain available for those who need them.