Thesis: 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, it shows that every single hour spent in the classroom studying mathematics generate a significant improvement in students' math performance. Second, it shows that the productivity of instructional time strongly relates to the implementation of interactive teaching practices, which require student active participation in the lesson. More precisely, each hour spent with a teacher putting a high weight on this kind of practices is 2 to 3 times more productive than an hour spent with a teacher putting a higher weight on traditional practices, such a teacher lecture. The second chapter of this thesis studies the impact of a public policy aimed at improving teachers' practices, namely the individual teacher evaluation system in French secondary education. In this chapter, we show that students' performance at the end-of-middle school national exam significantly improve after the evaluation of their math teacher, not only for students taught by an evaluated teacher the year of the evaluation, but also for students taught by the same teacher on subsequent years, suggesting a long-lasting improvement in teacher pedagogical skills. These positive effects persist over time for students, who not only perform better at the end-of-middle school exam but also choose more often and graduate more often from the science track in high school. In addition, the positive effects of teacher evaluation are particularly salient in education priority schools, in contexts where teaching is often very challenging.The third chapter of this thesis investigates the effect of school peers' gender on students' performance and educational careers in French middle schools. First, it shows that the proportion of female peers' in middle school has persistent effects on students' educational careers as it not only affects students' test score at the end-of-9th-grade national examination, but also influences their track choices and high school graduation rates several years later. Second, it shows that a larger share of girls in the classroom has positive effects for girls and negative effects for boys. More specifically, it reduces girls' dropout rates and increases their probability to graduate from an academic track in high school, especially in the scientific track, while it increases boys' probability to attend a vocational school after 9th grade and decreases their high school graduation rate.