Many schools and school systems have been deliberately working towards full implementation of Assessment for Learning for more than a decade, yet success has been elusive. Using a leader's implementation of Assessment for Learning in one school as an illustration, this article examines eight positional leaders' experiences as they implemented both the "spirit and the letter" of Assessment for Learning at all levels. This longitudinal qualitative research study draws on the experiences of leaders from Alberta, British Columbia, Germany, Georgia, Hawai'i, Manitoba, New Zealand and Ontario. The authors identify five findings that show how positional leaders use Assessment for Learning as the focus for system-wide change, as well as the change process itself.