This volume represents the output of a yearlong effort to clarify and firm the conceptual base that underlies educational RDD&E. It contains three commissioned papers authored by Drs. Hendrik D. Gideonse, Gene V Glass and Blaine R. Worthen, and by Leslie J. Briggs and one paper prepared by H. Del Schalock and G. Roger Sell of the staff of the Oregon Studies. The volume also contains a formal critique of each paper, an author response to each critique, and an introductory and summary critique of the papers as a set. Individually, the papers deal with one or more aspects of the domain of educational RDD&E. Collectively, they deal with the domain as a whole. As a set, the conceptual papers and their critiques are intended to serve as (1) a benchmark document with respect to the conceptual structures underlying educational RDD&E, (2) a primary reference for persons entering the field of educational RDD&E, and (3) a stimulus to the continued dialogue that these papers have only begun. Related documents are EA 004 582-584 and EA 004 586-589. (Author/JH)