Despite all the speeches, articles, and meetings about data-based instructional decision making, the author's observation after more than 20 years of working with middle and high school teams is that teachers and administrators often make important instructional decisions on the basis of historical precedent, anecdotal information, experience, or intuition, rather than by using information they have collected in a systematic manner. This article presents a six-step process to guide teachers in the use of data-based inquiry that focuses on students' current performance levels and actions that teachers may take to improve them. (Contains 2 figures.)