This paper is concerned with the operation of Junior Secondary Schools in France. Students' school careers have been analysed in three sequential and cumulative components: student progress in learning in the junior secondary school, student grading by teachers, and student streaming, i.e., admission, or not, into a general form 3. For each of the three mechanisms described above, the authors examine whether they are influenced by the schooling context, which schooling context (school and/or classroom), and which characteristics of those contexts it is relevant to consider. Finally, they focus on the process by which the large social inequalities visible after the pupils have been streamed (at the end of form 2) have been generated.