Background: In most studies in the classroom context, the student is generally only one variable in the analysis of the effects of the teacher's work. Our research was based on the postulate that the student's activity is basically autonomous, i.e. irreducible with the influence that the teacher has. This is why we propose to analyse the dynamics of students' activity in the PE lesson by adopting their point of view, i.e. starting from their meanings which emerge in the situation. We adopted a French socio-cognitive model: the "course of action". Purpose: This qualitative study was interested in the activity of two students (their typical concerns and their relations with mobilized knowledge) when they play face-to-face in table tennis. The first objective was to provide detailed information about students' typical concerns in PE in relation to their mobilized knowledge. The second objective was to contribute to a reflection on the intervention in PE, and in particular in racket sports. Participants and setting: Four 11th graders (two girls and two boys) from the same class in a rural secondary school in France meeting weekly for two hours of PE over the year. Intervention: A study of the activity of two out of four students (i.e. a dyad) in one of the 10 lessons of a cycle in table tennis, then a study of the other dyad in the following lesson. Voluntarily, the researchers did not take part in the design of the lessons of the cycle. They also limited the study to the specific periods when the two students played face-to-face. The first lesson privileged cooperative tasks whereas the second was focused on competitive tasks. Data collection: Three kinds of materials were collected during each lesson: (a) a video and audio recording of the students' activity during the lesson; (b) a self-confrontation interview with the students after the lesson; and (c) complementary ethnographic notes. Data analysis: It consisted of cutting the flow of activity into Elementary Units of Meaning (EUMs) that the students used to think and act. The data were analysed in three stages: (a) the construction of a two-level protocol, confronting the observation and interview data; (b) the identification of the EUMs; and (c) the identification of the series and archetypal series (larger units which gather the EUMs of which the concerns are the same). Findings: Separate results were presented in the analysis of both dyads. They showed: (a) components that were shared by the students of the same dyad in both case studies; (b) but no common components between both students' dyads. Discussion: The results were discussed on two levels: the first part concerned common features and differences in students' activity within and between the two dyads. It shows that it is important to understand that the students share certain concerns in similar tasks (in particular when they play face-to-face). In addition, it is important also to note that there are no common concerns between students who played in tasks of opposition and students who played in tasks of cooperation. The second level drew instructional implications from this research. We proposed to include systematically three dimensions in each task: tactical project, learning and pleasure. (Contains 8 tables and 1 note.)