Background: Teachers' roles in the emotional socialization of preschoolers have been less studied. Less attention has been given to the contributions of both child- and teacher-level variables. Objective: This study aimed at exploring the association between child- and teacher-level factors with growth in children's emotion regulation (ER) and emotion knowledge (EK). Method: We used hierarchical linear modeling and two-time-point (fall & spring) data consisting of 187 Taiwanese preschool children and 15 teachers. The child-level predictors included temperament characteristics and how the child's negative emotion is responded to with six aspects of the Coping with Children's Negative Emotions Scale (CCNES). The teacher-level variables consisted of teacher-reported reactions to negative emotions of children and duration of the teacher-child interaction as a group. Results: ER growth was predicted by three child-level predictors--teachers' punitive reactions to an individual child were negatively associated with, whereas children's negative affectivity and effortful control were positively associated with the change in ER. EK growth was predicted by both child- and teacher-level predictors--children's surgency/extraversion and teachers' minimization reactions to children as a group were negatively associated with, whereas both group-level child-teacher interactions and expressive encouragement were positively associated with EK growth Conclusion: This study supports that teacher's individual-level punitive reactions to a child's negative emotions negatively predicted ER growth, and that teacher's group-level minimization reactions negatively predicted, whereas group-level expressive encouragement and child-teacher interactions positively predicted children's EK growth, indicating children could put together repeated experiences of watching other children's emotions being reacted to.