The aim of this research is to study the efficiency of curriculum development services by taking opinions of people who work at those areas in private schools in Istanbul. By this method, the condition of limited school-based curriculum development studies are wanted to be shown. It is a case study, which is a pattern of qualitative research designs. The study group consisted of eight curriculum development staffs from seven different schools which had curriculum development service in 2015-2016. A semi-structured interviewing form which consists of six questions was prepared as data collecting tool and face to face interviews were made. Data were analyzed by content analysis method. According to the findings of research, half of the staff of curriculum development service stated that they gave equal importance to all four element of instructional programs, while the other half stated that they conducted active studies at evaluation with learning situations or just evaluation. Also it was detected that curriculum development specialists, who found their studies insufficient, were worked in tasks which they were not responsible for, and those people had active role in evaluation studies. Some of the staff of curriculum development service who thought all their needs are met and who had the support of school management find their studies sufficient. None of the curriculum development service staffs say that instructors do not contribute to the program development process. That situation shows that when proper conditions are met, instructors contribute at curriculum development service studies, in some methods differ from school to school.