The purpose of this study was to determine if the Primary Individualized Reading Divided Day (PRIMIR D/D) Program and the non-PRIMIR D/D approaches are effective in the Seattle school system; does the operation of the PRIMIR D/D program justify startup expenses and maintenance costs; is there reason for modifying, continuing, or eliminating the PRIMIR D/D or the non-PRIMIR D/D; and is the operation worthy of dissemination. The PRIMIR program is a method of individualizing the primary reading program through the use of a basal reader as a skills strand supplemented with paperback books and other reading materials to extend skills and efficiency. Over 600 first grade students participated in this experiment to determine the merits of individualized reading. Three experimental groups were formed: divided day with PRIMIR, divided day without PRIMIR, and a control group of similar socioeconomic and achievement level makeup. The results indicated the PRIMIR D/D students showed significant reading achievement gains over the non-PRIMIR students, who showed superiority over the control-traditional students. (WR)