Through the use of explicit theories in the design and analysis of teaching, Learning study can be used to generate theory-based and theory-generating results, which are possible to evaluate in a systematic way. The aim of this presentation is to discuss in what way, and to what purpose, theories of teaching and learning can be used in a Learning study, as well as what the characteristics are of those theories of teaching and learning that can be used for different purposes in Learning study. A study that explores qualitative differences in upper secondary school students’ conceptions of justice, in the subject of civics (Tväråna, 2014), is used to illustrate how a deeper knowledge of students’ conceptions of a specific subject content can be explored using phenomenography (Marton, 2014; Marton & Pong, 2005). The study is based on empirical data from seven interviews and written pre- and post-tests as well as recorded and transcripted material from nine research lessons in three Learning Studies. The study analyses students’ conceptions of justice, as well as students’ experiences of what it means to reason in civics.