There is a demand for educational research that addresses questions found in teachers' practice. This line of research can be referred to as practitioner research, and it is motivated by the realisation that teacher professionalism is one of the most influential factors in determining student achievement. One question is whether the primary purpose of practitioner research should be to improve teaching practices, or to contribute to theoretical knowledge. Some argue that the primary concern should be contributions to changing practices, whereas others suggest that contributions to theory are equally important. The purpose of the article is to discuss how Learning study, regarded as a clinical research practice, can contribute to developing teaching practices and theory of history didactics in conjunction. Learning study is commonly described as an interventionist, iterative and collaborative research approach, focusing on the teaching of an object of learning, which in this case was the learning of primary source analysis in history. Examples of how the Learning study contributed to practice and theory are presented. Contributions include the suggestion that knowing primary source analysis involves the ability to distinguish and separate three critical aspects in a temporal, human and contextual dimension, and that the students' personal perspectives are vital and should be regarded in the design of tasks and teaching. Based on the findings it is argued that practitioner research could aim at developing educational practices in conjunction with contributions to theory, and that practice and theory are necessarily entwined in the research process.