Journal article: In France, secondary school teachers are evaluated every five to six years by senior experts from the Ministry of Education. These evaluations involve the supervision of one class session, a debriefing interview and the writing of an official evaluation report. Their results are used to determine teachers' career advancement. We show that these repeated evaluations help improve teacher effectiveness (as measured by their students' performance) at all stages of their career. The impact on student performance is particularly strong in priority education schools and remains significant several years after students leave middle school. Evaluators' feedback likely plays a key role in improving teacher effectiveness.