After first glancing at previous research suggesting that schools (and principals) had little effect on students, this research review focuses on six research studies that suggest the opposite: schools (and their principals) can make an important difference in student achievement. The review highlights Michael Rutter's three-year study of British ten-year olds, which concluded that the "ethos" or norms of a school exert more influence on students than any other factor. Also discussed is Wilbur Brookover's study of Michigan elementary schools that reached a similar conclusion: a successful school has a climate that furthers success. These findings are seen to support those of Gilbert Austin, who found in addition that unusually successful schools all had a principal or other leader who was exceptional. Ronald Edmonds, who reviewed studies of effective schools, is also cited as finding that strong administrative leadership is the most important factor in school effectiveness. Finally, two other studies are briefly mentioned that emphasize the importance of leadership to school effectiveness. The review concludes that schools do positively affect the achievement of students by creating norms that support achievement and that the person who has the most influence on these is the principal. (Author/JM)