School-based day treatment is an intensive mental health service for children with social, emotional, and behavioral difficulties. Research on day treatment is scarce and descriptions of program models are lacking. We used stimulated recall interviews to explore the moment-to-moment processes and strategies of classroom staff in a day treatment program for children in kindergarten and Grade 1 in Canada. Several processes and strategies used by staff emerged from the thematic analysis of the interviews. These included a process of individualized intervention, characterized by a continual and cyclical process of attunement, responsiveness, assessment, and evaluation, using a team-based approach, noticing positives about children, a climate of positive relationships, staff regulating their own emotions, being flexible while also being firm and consistent, and seeing children from a developmental perspective. More specific strategies used by staff (e.g., token economy) also emerged from the interviews. Implications for future research and teacher training are discussed.