Researchers and educational software developers have talked about building authoring tools for intelligent tutoring systems (ITSs), adaptive and knowled- based instructional systems, and other forms of advanced-technology learning environments (ATLEs) ever since these forms of educational software were introduced in the 1970s. The technical complexity and high development costs of these systems contrasts sharply with the common picture of education as a "home grown" activity performed by individual teachers and trainers who craft lessons tailored for each situation. There have been two...