In recent years, numerous studies have delved into the impact of universal and evidence-based Social and Emotional Learning (SEL) programs within the spectrum of pre-primary to secondary education.  Implementation nuances  significantly influence these programs’ efficacy, with school leaders playing a pivotal role in facilitating their integration into diverse educational contexts. This article presents a multiple case study examining the implementation of the Trabün SEL program in two schools of different sizes. Using a mix of individual and group interviews, this study aims to pinpoint key differences in factors influencing implementation. It also explores the strategies used by school principals and program heads to support Trabün SEL program implementation in their respective schools. The results show variations in the commitment and motivation of school principals, the willingness of teachers to participate, communication dynamics among participants, the working environment, and the strategies employed for program support and monitoring. The conclusions of this report carry significant implications for educational institutions promoting SEL      programs, emphasizing the importance  of effective communication management and the need for diversified support strategies and monitoring approaches tailored to schools of different sizes.In recent years, numerous studies have delved into the impact of universal and evidence-based Social and Emotional Learning (SEL) programs within the spectrum of pre-primary to secondary education.  Implementation nuances  significantly influence these programs’ efficacy, with school leaders playing a pivotal role in facilitating their integration into diverse educational contexts. This article presents a multiple case study examining the implementation of the Trabün SEL program in two schools of different sizes. Using a mix of individual and group interviews, this study aims to pinpoint key differences in factors influencing implementation. It also explores the strategies used by school principals and program heads to support Trabün SEL program implementation in their respective schools. The results show variations in the commitment and motivation of school principals, the willingness of teachers to participate, communication dynamics among participants, the working environment, and the strategies employed for program support and monitoring. The conclusions of this report carry significant implications for educational institutions promoting SEL      programs, emphasizing the importance  of effective communication management and the need for diversified support strategies and monitoring approaches tailored to schools of different sizes.