When evidence-based prevention programs are implemented in schools, adaptations are common. It is important to understand which adaptations can be made while maintaining positive outcomes for students. This preliminary study evaluated an abbreviated version of the Promoting Alternative Thinking Strategies (PATHS) Curriculum implemented by school-based mental health clinicians in preschool/kindergarten classrooms. Results suggest that students (N = 80) demonstrated increases in emotional understanding and prosocial behavior. Children with low initial levels of problem behavior demonstrated large and continual increases in prosocial behavior over the entire course of the intervention, whereas children with high initial levels of problem behavior only demonstrated small gains in prosocial behavior during the first half of the intervention. These preliminary results support the general effectiveness of the adapted intervention, but also suggest the need for additional intervention to produce meaningful and sustained behavioral gains for higher-need students.