This paper shows how a pre-service physics teacher (Alicia) developed her knowledge about students through her first year of pre-service experiences. For that purpose, we adopted a narrative inquiry methodology: stories were used as a rhetoric resource to show Alicia's knowledge, and, simultaneously, as the object of inquiry and the research method. The sources used to collect data were audiotaped interviews, videotaped teaching episodes, researcher's field notes and the teacher's written documents. The data analysis revealed some characteristics of Alicia's developing knowledge about her students, and allowed us to document this development as a three-stage process. In the first stage, she got acquainted with her students' motivation (motivated-unmotivated), academic performance (high-low) and classroom behaviors (positive-negative). In the second stage, Alicia learned some effective strategies to motivate her students, and more appropriate ways to interact with her students to promote learning within them, especially with those that made her feel an emotional, cognitive and relational security or insecurity. In the third stage, the teacher learned about some students' difficulties to perform certain typical tasks of physics classes (solving physics standardized problems and reading physics textbooks); as well as their difficulties to understand physics concepts (such as distinguishing and relating every day language and scientific language or inferring meaningful relations between scientific concepts). We discussed some of the implications for the initial education of physics' teachers.