The Human Capital Theory developed by Gary Becker in the 60's substantially widened the area of investigation of economics. Over the last two decades, many studies in the economics of education intended to identify the characteristics of an educational system which enable individuals to acquire as much skills, knowledge and information as possible. This thesis contribute to this literature by studying two aspects of the educational environment that has particularly attracted economists' attention over recent years: teacher productivity and peer effects in the classroom. The first chapter of this thesis investigate to what extent teaching practices implemented by math teachers in the US relate to their students' math performance. First, i...