This paper reflects on the author's participation in two government-sponsored educational software development projects that used a holistic design paradigm in which classroom formative assessment and teacher input played a critical role in the development process. The two project were: R-WISE (Reading and Writing in a Supportive Environment)--a learning environment to teach writing at the ninth and tenth grade level, and BioBLAST (Better Learning through Adventure, Simulations, and Telecommunication)--a content-rich learning environment that mirrors research being carried out at several NASA centers. In both projects, high school teachers were part of the design team from the beginning, and both alpha and beta versions were field-tested in classrooms. Characteristics that classroom experts believe should be instantiated in truly effective educational software are described. Features that enhance the teacher's effectiveness in the learning process by allowing them to become mentors and facilitators include: developing bridging activities for clarifying and reinforcing concepts; using "artifacts" to foster learning; and sustaining the sense of a community for scientific inquiry. Features that encourage students to become active participants in problem-based learning include: improved strategies for inquiry; enhanced communication and publishing competencies; and increased understanding of the relationship between information manipulation and concept formation. (AEF)