In the Canton of Geneva, during the compulsory schooling years, the Education Services make use of external assessments. Amongst other things, these aim to evaluate the knowledge and abilities acquired by students in order to either award promotion and/or qualifications or advise on appropriate career paths. This brings many issues to the fore. To what extent do the results achieved during these external assessments depend on the students’ individual characteristics and also on the characteristics of the classes in which they are being taught? Are these characteristics constant throughout one’s compulsory schooling? We shall try to answer these questions by using linear hierarchical models (also called multilevel analyses) based on results achieved in June 2006 in the particular area of reading comprehension.