Although potentially powerful for educators, the construct of teacher reflection has become diluted, rendering teacher engagement with meaningful reflection problematic. This article presents a theoretical framework that divides teacher reflection into two broad categories. The first and most common "incident reflection" occurs as specific incidents or episodes unconnected to future activity. The second "process reflection"--based on the work of John Dewey and Donald Schon--connects reflective incidents into a cyclic progression that refines ideas through experimental action. I examined the reflective activity of a group of prospective secondary mathematics teachers as they jointly planned a public school lesson to illustrate how incidents of reflection can be refined and linked into more powerful and purposeful progressions of ideas. I conclude with implications for mathematics teacher development.