Success of curriculum reforms calls for both collaborative learning and unlearning processes. Focusing on the latter, school doubting process, an innovative term, is used in this paper as an active framework for organisational unlearning through which educators question their existing mind-sets and unfreeze old approaches to teaching and learning. This qualitative study explores how high school principals shape a school doubting process during the implementation of a national curriculum reform. The study analyses qualitative data from semi-structured interviews with 22 Israeli high school principals who have implemented a national curriculum reform from all school districts. The findings indicate two major themes and sub-themes: (1) Nurturing a collective unlearning culture: (a) restructuring school thinking; and (b) creating safe time and space for school doubting; (2) Building school capacity: (a) creating collective opportunities for knowledge and skill development; and (b) encouraging shared responsibility for innovation.