The aim of this work is to understand and explain how external evaluation determines the pedagogical practices of terminale teachers. To this end, we observed the actual teaching practices of these teachers in the classroom, and interviewed them in order to gain insight into their logic and reveal their pedagogical practices. From their discourse, teaching and assessment practices, we highlighted certain interferences between the pedagogical and administrative objectives of the national exam, and the teachers attribute different meanings to the results of this exam, as they are not credible for some; they proceed to train learners for the national exam through increased transmission of cognitive and methodological knowledge useful for the exam, so classroom assessment is merely a kind of placement of learners in situations similar to those of the national exam.