Student well-being is a major issue for School and society. This doctoral thesis aims to identify if teachers’ practices can contribute to its improvement. Based on achievement goals theory, our studies examine wether practices emphasizing mastery and improvement (mastery structure) or emphasizing elitism and social comparison (performance structure) are linked to student well-being, measured by emotions at school, life satisfaction and depression. Our approach is characterised by the use of multivel statistical models which allow to draw more valid conclusions about effects of the school environment. Moreover we seek to make a contrinution to the understanding of underlying processes. Finally, other teachers’ practices and the quality of peer relationships are also taken into account.