This study addresses two questions: (1) Why do fourth grade students in Rhode Island perform better on the Iowa Tests of Basic Skills (ITBS) than eighth grade students?, and (2) Why do Rhode Island parochial students perform better on the ITBS than public school students? The examination of both questions focused on three areas: school setting factors, population factors, and psychometric and test-intrinsic factors. Data were collected from interviews with teachers and administrators, a teacher questionnaire, demographic and test score files from the Rhode Island Department of Education, and the ITBS technical manuals. Public school fourth to eighth grade differences were substantiated and attributed to differences in teacher perceptions of parental support, time spent in teaching reading, rate of absenteeism, and teacher perceptions of the effectiveness of discipline procedures. Likewise, parochial/public school differences were attributed to differences in the percentage of female students, teacher perceptions of parent support and student motivation, fathers' occupational status, time spent in teaching basic skills, pupil/teacher ratios, rate of absenteeism, and teacher perceptions of the effectiveness of discipline procedures. Complete data are available in the final report (TM 007 157). (BW)