Problem-based learning (PBL) is a pedagogical strategy that centers learning activities around the investigation and development of solutions to complex and ill-structured authentic problems. It requires additional support and resources for students and instructors to use it in schools. Computer-based interactive learning environments have been used to provide students authentic and supportive settings for PBL These systems, however, require significant up-front development effort before they can be put into use. In this paper, we describe an incremental model that allows instructors to author the learning environment during real use. In our model, an instructor is part of the feedback loop, complementing system feedback and collecting materials to be incorporated into the system. By working within the system, the instructor can observe detailed traces of student learning activities in the system and provide individualized coaching and critiquing. We describe our experience in developing Corrosion Investigator, a web-based learning environment, as an exemplar of our model. We focus on how the system is designed to facilitate instructor involvement and support incremental authoring. We present empirical results showing materials collected through use and benefits to the students and teachers.