The recommendation to study statistical variation has become prevalent in recent curriculum documents. At the same time, research on teachers' knowledge of variation is in its beginning stages. This study investigated prospective teachers' knowledge in regard to a specific measure of statistical variation that is new to many curriculum documents: the mean absolute deviation (MAD). Seventy-six prospective teachers participated in the study. Participants exhibited various procedural and conceptual characteristics in their thinking about the MAD. The majority were able to successfully select and carry out a procedure for computing the MAD. However, some had difficulty dealing with procedures for absolute deviations, and others confused the procedure for the MAD with the procedure for a different descriptive statistic. Conceptually, participants offered a variety of interpretations of the MAD, with some demonstrating deep understanding of the measure and others demonstrating shallower understanding or misconceptions. Those who demonstrated the strongest conceptual knowledge of the MAD also exhibited sound procedural understanding, suggesting that the two types of knowledge are intertwined in the process of fully understanding the measure.