Teachers are important socialization agents as children develop ways to self-regulate their emotions, and this development is considered as an important achievement in preschoolers. The present study investigated two main questions: (1) How preschool teachers change their emotion coaching and co-regulation behavior as children age and as the children's emotion regulation improves, and (2) how teachers' co-regulation is linked to children's self-regulation. Preschoolers aged 4-6 years (n = 28) and their teachers (n = 9) from three preschool classrooms participated in the study. Based on extensive video recordings of everyday interactions in the classroom, the children's emotionally challenging episodes were identified and analyzed. The results indicated that teachers' emotion coaching and co-regulation occurred more frequently when the child was younger. For older children, teachers showed more intense co-regulation if co-regulation occurred. The better the emotion regulation of the child, as rated through the teachers, the more often teachers started co-regulation by giving unspecific, meta-cognitive prompts. Furthermore, after controlling for age and reported emotion regulation, co-regulation was systematically related to observed selfregulation within episodes. Overall, the results support the assumption that teachers' co-regulation is adjusted to children's developmental level and contributes to their development of self-regulation of emotions. (author abstract)