Assessment has been a central element of French public educational policy over the past two decades. Based on national surveys of students and schools results, assessment is also increasingly present within the schools themselves. At the local level however, it deals with different and specific issues and problems, by compelling educative actors to face a synthetic quantitative image of their activity, by attribute new tasks to them, and involving complex relationships between action and outcomes. To understand the consequences of the practices of local assessment, we will rely on a qualitative survey of the daily work of a principal and his team, in a secondary school located in a “positive discrimination” area, in the north of France, observed during the 2004-2005 academic year.