Motivation plays an important role in students’ school behavior, and research has established that students’ learning environment experiences such as teachers’ behavior toward them contribute to their motivation and behavior at school. Self-determination theory offers an interesting frame of reference in the study of the relationship between students’ learning experiences at school and their school behavior. Considering three basic psychological needs, the SDT points to the importance of nutriments and support in the social environment in order to allow growth in (...) motivation, engagement, and well-functioning. In addition, thwarting these needs is supposed to contribute to maladaptive functioning. Teachers can play an important role in the fulfillment of students’ basic psychological needs by delivering support ; however, controlling instructional behavior, chaos in the classroom, and teacher rejection and neglect are supposed to be a treat to the fulfillment of students’ basic psychological needs. In the current innovative longitudinal study, teachers’ need-supportive behavior as well as teachers’ thwarting of these needs are considered and their relationship with students’ academic engagement and procrastination behavior is studied. In addition, attention is paid to differential effects of teachers’ behavior with regard to boys and girls. Participants were 566 students belonging to 20 mathematics/English grade 1 secondary education classes in the Netherlands. Multilevel analyses revealed evidence for the importance of both teachers’ need-supportive and need-thwarting behaviors in relation to students’ academic engagement and procrastination behavior. In addition, the findings revealed that teachers’ need-supportive behavior is more important for students’ academic engagement, while teachers’ need-thwarting behavior has larger effects on students’ procrastination behavior. Furthermore, evidence was found that boys often seemed to be more sensitive to their teachers’ behavior than girls. The findings highlight the importance of both teachers’ need-supportive and need-thwarting behaviors in daily classrooms and contribute to deepen our insight into and understanding of factors leading to adaptive and maladaptive functioning of boys and girls in relation to learning tasks at school. (shrink)