ILE (Interactive Learning Environment) is a highly multidisciplinary research domain. Design of such systems can not be done exclusively by computer scientists. Educational scientists, teachers who will prescribe the system and learners who will use it should also be involved in ILE design. Management of relationships between on the one hand computer scientists, and on the other hand other members of the design team is not obvious. We propose a design method, the differentiated design, which aims to ease the management of these relationships by using different design methods adapted to each type of non computer scientist members of the design team. In this paper, we then present our differentiated design method and show how we applied it in the PÉPITE project.