Although historical thinking has been the subject of a substantial body of recent research, few attempts explicitly apply the results on a large scale in North America. This article, a narrative inquiry, examines the first stages of a multi-year, Canada-wide project to reform history education through the development of classroom-based assessments. The study is based on participant-observations, documents generated by the project, and interviews, questionnaires, and correspondence with participants. The authors find impediments – apparently surmountable – in teachers' application of potentially difficult concepts, and in their organizational resistance.