The objective of this study was to gain knowledge concerning what up-per secondary students need to learn to be able to construct historical explanations while working with historical sources. The study also explored how teaching could be designed to enhance student’s capabilities. The history didactical framework took its departure in the British Historical Thinking-tradition and the methodology was based on Learning Study, an iterative research method for analysis and enhancement of teaching and learning. Empirical data originates from one Learning Study undertaken in an upper secondary school performed in cooperation with three teachers teaching three different classes. The bulk of data consists of student interviews, video recordings from research lessons and essay texts performed by the students before and after research lessons. Variation Theory was used to analyse teaching and learning with the purpose to identify critical aspects of what characterizes the capabilities and what the students needed to learn to reason about causation, interpret and use historical sources. The historical content was framed on the late 19th century phenomenon known as The Scramble for Africa where the students were supposed to reason on the causes for thescramble while working with a variety of primary sources. The methodological design of the research-lessons was based on a combination of principles from Variation Theory and Learning Activity with the ambition to form an educational practice that would allow students to discern the critical aspects and advance their learning. The results show that the students who participated in this study needed to distinguish the following critical aspects to be able to construct Historical Explanations when working with sources: Cause To distinguish temporal aspects of historical change not to confuse causes and consequences. To distinguish that historical change are caused by societal structures and intervention by historical actors and do not occur by itself. To distinguish that historical change predominantly have their origin in several causes and cannot be reduced to single causes. To distinguish that historical explanations need support from evidence. Interpret and Use Historical Sources To asses sources critically rather than view them as neutral information. To contextualize sources to avoid presentism and literal interpretations. To corroborate sources to be able to validate claims and present different perspectives in a historical explanation. To see that values and limitations of sources depend on the historical questions we seek an answer to. To distinguish the difference between authentic sources and reliable claims.