A diagnostic methodology for large-scale assessment was employed to compare performance on a national test in mathematics of representative samples of Jewish and Arab 8th graders in Israel in order to shed light on a previously identified large achievement gap between these 2 populations. The results revealed significant differences between the 2 groups in patterns of strengths and weaknesses with respect to content, process, and skill/item-type attributes, indicating different paths for remedial interventions. (Contains 3 tables, 2 figures, and 2 notes.)