Similar to educators in mathematics, science, and reading, history educators around the world have mobilized curricular reform movements toward including complex thinking in history education, advancing historical thinking, developing historical consciousness, and teaching competence in historical sense making. These reform movements, including the Common Core Standards, are beginning to include historical thinking. Despite these developments, inclusion of historical thinking in assessments has been slow: The great majority of history assessments, both large-scale and classroom-based, still focus on fragmented pieces of information. In this article, we discuss the challenges in assessment of historical thinking, describe how these issues were dealt with in a 1-hr test of students ability to reason about "enemy aliens" in Canada during World War I, and make recommendations for future assessments.