This paper aims to find out what processes contribute to horizontal (between employees) and vertical (between employees and their supervisor) shared perceptions of supervisor support by public frontline supervisors. Informed by a multilevel qualitative study among supervisors and teachers in public secondary schools, we develop theoretical propositions regarding these processes. We propose that employees’ expectations based on experiences with previous supervisors can decrease horizontal shared perceptions. Subsequently, a contingent or consistent approach to supporting employees contribute to the development of horizontal and vertical shared perceptions, depending on the legitimacy attributed by employees to the reason behind this approach. Over time, supervisor support experienced by employees at meaningful work-life events contributes to the emergence of horizontal and vertical shared perceptions. This research shows that instead of merely looking for correlates of shared perceptions, scrutinizing the processes that contribute to horizontal and vertical shared perceptions increases our understanding of this complex phenomenon
