Previous research has shown that teachers differentiate their behaviour based on their expectations of students. Self-determination theory (SDT) makes explicit how teacher behaviour relates to students’ motivation and engagement, namely, via need-supportive teaching. In the present study, we combined both research traditions and examined associations of teacher expectations with need-supportive teaching and thereby students’ motivation and engagement. Two-hundred-and-seventy-six secondary school students and their teachers (N = 11) completed questionnaires. The results indicated that teacher expectations were moderately but positively associated with students’ intrinsic motivation and engagement, and negatively with amotivation. These relationships were fully mediated, although with small effect sizes, by need-supportive teaching. These findings highlight the value of combining research on teacher expectations and SDT, to gain further understanding of how teacher expectations may cause teachers to provide more need support to some students than to others, thereby affecting students’ motivation and engagement.