Performance of educational administrators will affect development of emotions and values of students. This could be considered as one factor with regard to hidden curriculum. This research study aimed to examine the role of principals on the value system of students based on the Graves' model. Using a qualitative approach, this case study was conducted in a girl’s high school in Mashhad, Iran. Data were collected through semi-structured interviews and observation of physical arrangement, social and interpersonal interactions between principal, vice-principals, and students, as well as narratives and student portfolios. Accreditation was carried out using triangulation, re-evaluation, and recoding. Results indicated that involvement of principals in planning would result in substantiating value system of students at levels one to four according to the Graves model whereas participants failed to reach levels of spirituality, congruence, rationality, concern for society.