Working with sources in secondary school history education has become a common practice over the last few decades. However, researchers have concluded that teaching practices relating to the educational use of sources cause difficulties. Teachers often only examine sources for/in relation to their content, and tend to ignore author and context information in the analysis of the source. This paper reports on an empirical study focusing on how primary sources are dealt with in Flemish secondary school history education, in which the standards only make general reference to the use of sources. It focuses on whether primary sources are used to prompt reasoning with and/or about sources, and includes an examination of both the kind of primary sources that are used, and the provided source and context information. 88 classroom history lessons in the three stages of secondary education, involving 51 teachers, were observed and analyzed. Analysis shows that primary sources play an important part in the lessons. Overall, 21% of all primary sources were used for illustration, 55% to reason with sources and thus to foster students’ substantive knowledge, and 24% to reason about and thus foster students’ strategic knowledge. Important differences and similarities regarding the educational use of primary sources between the three stages of secondary education are also found, and further explained and discussed.