This research study involves an in-depth evaluation of TAMAM capacity building model in one of its participating schools and follows a qualitative case study design that also adopts a collaborative evaluation study. It has a threefold purpose: (1) to examine the effectiveness of TAMAM’s capacity building model in reaching its desired changes in the professional knowledge, skills, and attitudes of the TAMAM school leadership team members, (2) to explore its impact on their motivation, and (3) to explore its impact on the school organizational learning in terms of its professional norms and structure. The case school is a private non-profit school that joined the TAMAM project in the year 2013-2014 and volunteered to implement its newly designed capacity building program. The case school completed one full cycle of TAMAM’s school improvement journey in 2017- 2018. The participants in the study will comprise all the individuals who took part in the capacity building activities in the TAMAM project at the case school between 2013-2019, the school lead team members, the head of the advisory board of the case school, the school principal and the Project Steering Team (PST) at the American University of Beirut. Diagnostic checklists, individual interviews, focus group interviews, as well as relevant school documents, were the sources of data. The findings of the study reveal that members’ participation in the TAMAM project resulted in considerable growth in their acquisition of the knowledge, skills, and attitudes of TAMAM competencies and stations of its school improvement journey. TAMAM capacity building model seemed to have reached to a large extent, its desired changes in the professional learning and capacity building of members that enabled them in leading effective and sustainable school-based improvement. Findings also showed that the lead team participation in the TAMAM project had a mostly positive impact on strengthening the team motivation and sustaining their commitment towards leading improvement initiatives due to their increased feelings of competence, autonomy, and collaboration that subsequently increased their motivation and empowered them to be agents of change. Finally, findings also showed that the participation in TAMAM project had several impacts on the organizational learning manifested by a myriad of structural and normative impacts on the case school. Results reveal the effectiveness of TAMAM capacity building model illustrated in terms of the outcomes it achieved in building lead team members’ leadership capacities that prepared them and motivated them to lead school improvement and in terms of its alignment with what the literature proposes as effective professional development approaches that build leadership capacity for improvement. Drawn from the study results, recommendations for practice are suggested, and recommendations for research are also proposed.