This study explores the experiences of high school middle leaders implementing a generally outlined reform, which required educators to exercise judgment regarding how to meet the reform's goals. Exploring 65 middle leaders' perceptions regarding the implementation of the Meaningful Learning Reform in Israel revealed that they experienced two main challenges: the need for self-reliance, meaning that they had to follow their own discretion; and coping with ambiguity, meaning that they were required to operate under conditions of uncertainty. Through a sensemaking lens, this study broadens the currently limited knowledge regarding middle leaders' experiences with reform programs.