This study contributes to the investigation of the variability of the schooling effect on cognitive development between educational systems and its underlying factors, by focusing on 3 cases differing in the characteristics assumed to affect the magnitude of the schooling effect (the quality of the schooling and students' mean ability to benefit from their schooling): the United Nations Relief and Works Agency (UNRWA) educational system in the Palestinian refugee camps in the West Bank and the 2 sectors of the Israeli educational system: the Jewish and Arab systems. Congruent with our expectations, the highest absolute and relative effects of schooling were found in the Israeli Jewish system. In contrast, the results obtained in the 2 Arab systems, namely, the higher schooling effect found in the poorer and more oppressed refugee camps of the West Bank, are surprising and require further investigation.