We propose a teaching method that yields similar results to actual development projects instead of coordinating actual projects which require much labor and expense. Moreover, we propose a method of efficiently editing teaching materials from a real scale open source software product. According to this method, students can have experiences to make decisions with foresight in a realistic development process, and teachers can create teaching materials efficiently and make repeated use of them. Our method is suited to students who have acquired an understanding of object modeling and object-oriented programming but who have no experience of software development on a realistic scale.