This paper presents some thoughts on the production process of education indicators. First, it places indicators in education in the large field of social indicators. Second, we present the indicator as a statistic and describe what are the features of an indicator system. Then we discuss some suggestions and criterias that could be helpful in building an indicator system and the tensions at work when we want to build such a system. Finally we present a short analysis of different indicator systems, like those of OECD and UNESCO, that permits to illustrate what are the possible sources of contamination when results to standardized test are used as output indicators in an accountability view.