The Educational Technology Center (ETC) has devoted the last five years to studying ways of using the computer and other information technologies to teach understanding in science, mathematics, and computing in the nation's elementary and secondary schools. The Center's research has focused on targets of difficulty, topics and concepts that are both central to their disciplines and recognized by teachers and students as difficult to teach and learn. By seeking to apply new technological capabilities at these particular points in the curriculum, they have attempted to make a real difference in the ability of schools to educate students. From the beginning it was realized that making a difference in schools would require a different sort of research and development approach than had previously been tried in science and mathematics education. A framework and five-point focus has become the hallmark of the Center's work: (1) subject matter; (2) student's ideas about subject matter; (3) teaching for understanding; (4) technology; and (5) implementation. This document presents summaries of the work of individual research projects. Work is summarized for the first four years of research and the fifth year is presented and discussed with implications for practice and future research. (MVL)