Stemming from a study led in a vocational upper secondary school during the mobilization against the “CPE,” this article describes and explains the multiple and ambivalent attitudes of secondary school pupils towards the anti-CPE movement. From outspoken or discreet support to indifferent sidestepping or even ostentatious self-exclusion, these behaviors derive from legitimacy effects implied by the normal functioning of the school institution, which is to say from the obviousness of social boundaries that this institution guarantees.