The study attempts to examine the practice of effective principals’ instructional leadership in high schools at a time of curriculum reform with a cultural approach. The new curriculum encompasses not only knowledge, but also attitudes and behaviors. It also emphasizes the use of scientific approach and portfolio as a form of authentic assessment in the learning process. The research data were collected by interviewing principals, vice-principals and senior teachers at five referral High Schools in the Special Region of Yogyakarta, Indonesia. These schools are parts of pilot projects in implementing the new curriculum. The study uses qualitative research methods. This study revealed that instructional leadership is associated with curriculum reform, starting from a full understanding of the curriculum vision. It is realized in a conducive culture and climate, such as religious culture, discipline culture, literacy culture, creative and innovative culture in solving life problems, learning anytime and anywhere, doing a collaboration, joining fair competition, and caring for the environment. The habituation makes values, attitudes, and behavior applied not only in theoretical knowledge (memorization) and practiced in school but also brought by students to their families and communities.