This article presents a study examining the historical literacy skills of Finnish (N=86) and Californian (N=131) high school students. Our goal was to discover how students read and subsequently interpret historical documents. For this purpose we created a document-based task. We analysed the data by surveying how students interpreted the documents and used them in their texts. The students were capable of identifying the content of each document and most crafted coherent conclusions based on the given sources. The most problematic aspect of historical literacy in our study was contextualising documents. However, there were differences in the results for the groups. Among the Finnish high school students, the variation was great. Those students who mastered historical content knowledge also mastered historical literacy; those whose historical content knowledge or Finnish language skills were weak also had weak historical literacy. This polarization was not evident among the Californian students we examined. However, their disciplinary literacy skills were reduced to generic text skills; students took the document-based interpretation task as a reading comprehension task and did not evaluate the authors’ intentions.