Grade retention decisions are complex. It seems that a whole set of elements leads teachers to consider this measure as the advisable one to take. This article tries to understand and analyze this complexity. What is proposed is to analyze more thoroughly the action (process and formation) that leads to this judgment. What are the constituents that underlie the judgment in a decision of grade retention and which relevance do these various constituents have in the final decision? The empirical data was collected in interviews with 41 6th grade teachers (primary) in Geneva during the school year 2007-2008. Each teacher is questioned about a promotion and a grade retention decided the previous year. The interviews try to re-tie the decision-making framework of this in situ judgment. The question of qualification of this judgment as «professional» is then tackled in the final discussion.