We used cognitive developmental theory to examine teachers' perspectives on the use of pedometers in physical education. Twenty-six elementary physical education teachers participating in long-term professional development were observed and interviewed twice over 6 months as they learned to incorporate pedometers into their teaching. Data were analyzed via constant comparison. The teachers reported four significant shifts in their thinking and values regarding pedometers. First, at the beginning, the teachers predicted they would encounter few implementation challenges that they would not be able to overcome, but, after prolonged use, they voiced several limitations to implementing pedometers in physical education. Second, they anticipated that pedometers would motivate primarily higher skilled students, but found that lesser skilled students connected with them more. Third, they moved from thinking they could use pedometers to teach almost any content to explaining four areas of content that pedometers are best suited to assist in teaching. Last, they shifted from seeing pedometers as potential accountability tools for student learning and their teaching to identifying key limitations to using pedometers for assessment. Our discussion centers on connecting these findings to teacher learning and professional development, and on the implications for teacher educators and professional development specialists advocating pedometers in physical education.