The aim of this study is to explore the role of K-12 school principals' self-efficacy as an attribute for their leadership effectiveness in Lebanon. The Norwegian principal self-efficacy scale (NPSES) instrument was translated into Arabic and used to collect quantitative data from participants. Internal consistency of factors within this study was checked (24 items; [alpha] = 0.73). By comparing private and public schools in Lebanon, all located in the governorate of Mount Lebanon, the researchers revealed the extent to which principals' self-efficacy plays a role in their leadership. In addition, while no statistical difference was found between self-efficacy levels of private and public principals, females reported higher scores on the majority of the dimensions than their male counterparts in both types of schools. This study highlights the importance of the interaction effect of age and gender on self-efficacy levels. Moreover, it offers knowledge and practice to policy makers when recruiting principals or designing training programs. It also suggests the implementation of an in-house mentoring program to create school-school partnerships. Finally, this paper offers a platform for future researchers interested in principal self-efficacy in similar conflict-affected places with high economic depression. Limitations are further mentioned.