Children's social-emotional and cognitive development is enhanced when early childhood educators display positive affect and respond appropriately to children's needs. However, there is little research on factors that influence teachers’ positive affect in the classroom, such as past adversity exposure and promoting teachers’ well-being. The current study examined the interactive effect of teacher participation in a well-being program (Be Well Care Well; BWCW) and their exposure to adverse childhood experiences (ACEs) on changes in observed teacher affect over time within the classroom setting. Participants included 95 early childhood teachers who completed the ACEs measure, a live classroom observation before participation in activities, and a post-intervention observation. Multilevel modeling estimated the interactive effects of teacher ACEs, participation in BWCW activities, and time on the dependent variable (i.e., teacher affect). Results from the three-level random intercept model showed a significant three-way interaction. Individuals with a higher number of ACEs and lower participation in the well-being program showed a decrease in positive affect over time. This effect was not significant for teachers who reported fewer ACEs. Results indicate that the degree of participation in the well-being program was particularly salient for teachers with higher exposure to past ACEs. Findings suggest that fostering teachers’ physical health and well-being can enhance their affect and enthusiasm in the classroom setting, particularly for those with higher levels of past adversity exposure. (author abstract)