Mason et al. (1982) encourage the writing of one’s thinking to help one notice and thereby to learn from one’s experience. There are several things worth noting, Chapman PME 37 - 2013 2 - 155 particularly: key ideas; key moments that stand out in one’s memory; and positively what one can learn from this experience. To facilitate this process, Mason et al. suggest four key words to use in making notes and in one’s thinking: Stuck!, Aha!, Check, and Reflect. Whenever one realizes one is stuck, one writes down Stuck and why one is stuck. “For example: I do not understand . . .; I do not know what to do about . . .; I cannot see how to . . .; I cannot see why . . .” (p. 16). Whenever one gets an Aha, i.e., an idea or thinks one sees something, write it down. For example, “write down Aha and follow it with Try . . .; Maybe . . .; But why . . .” (p. 16). One then Checks any calculations or reasoning; any insight on some examples; that the resolution does in fact resolve the original question and Reflects on what happened. These key words provide a scaffold around which a resolution is built, and encourages checking and reflecting on one’s resolution, an essential ingredient for improving one’s mathematical thinking.