Present study aims to investigate the mediating role of school culture (SC) in the relationship between heads' instructional leadership (IL) and students' engagement (SE) at secondary school level. The target population was comprised of all secondary school teachers of district Punjab. Multistage sampling techniques were used to select the sample. The sample was consisted of 1016 secondary school teachers. Questionnaire was used to collect data. Structural Equation Modeling (SEM) technique was used to analyze the mediating effect. Results revealed that total effect of IL on SE is statistically significant ([beta]=0.655, t= 27.572, p= 0.000), while the direct effect of IL on SE becomes statistically in significant ([beta]= 0.109, t=1.480, p=0.139). However the indirect effect of IL on SE through the mediation of SC is statistically significant ([beta]=0.546, t= 8.662, p= 0.000). These findings show that school culture is a statistically significant mediator for the relationship between heads' instructional leadership and students' engagement.