Development has traditionally been seen as part of a one-way street running from the researcher to the practitioner. Studies of the "mutual adaptation" of development products undercut this view of development and suggest that it should be seen as a two-way street that takes into account the practical knowledge of teachers and administrators. A participant observer study of two efforts at "collaborative" development in the fields of basic skills and career preparation illustrate the kinds of practical knowledge that practitioners bring to the process and the changes in development processes that result. The study concludes that the practical knowledge of practitioners, linking agents, and developers all contribute to the development process. In addition, development products need to provide enough flexibility to encourage intelligent local adaptation, but enough guidance to really provide educators with new knowledge. (Author/PN)