The aim of this presentation is to show how results from a Learning study can contribute to knowledge building in the academic field of history didactics, regarding 16-17-year olds’ learning of primary source analysis. The research interest emerged from learning issues identified in practice by history teachers, but the question is topical in history didactics as well. The identified object of learning was the students’ ability to critically analyse and contextualise historical primary sources. A Learning study (Runesson et al, 2012), which is a theory-informed and interventionistic research methodology, was organised to explore the object of learning. A disciplinary approach to history teaching was adopted for assignments and lessons (Seixas et al, 2012). One result was the identification of three critical aspects of primary source analysis, e.g. that it is critical for the students to discern the subtext of the source. Critical aspects can be used for design purposes, but also to explore the students’ learning process, thus generating didactical knowledge. The paper exemplifies two such contributions through one of the critical aspects: firstly, how the critical aspect is discerned in social interaction, and secondly, how meaning is constructed in relation to the critical aspect.