A summary of the work of Reuven Feuerstein. Feuerstein and his co-authors define intelligence as a dynamic force that drives the human organism to change the structure of thinking in order to answer needs. They describe the specific skills of the three stages of thinking - the input and data-gathering stage; the processing stage; and the output stage - and show how student thinking can stall at any of these stages and how intentional mediation can help students restructure their thinking and improve their ability to learn.