Valerie Lee and Douglas Ready explore the influences of the high school curriculum on student learning and the equitable distribution of that learning by race and socioeconomic status. They begin by tracing the historical development of the U.S. comprehensive high school and then examine the curricular reforms of the past three decades. During the first half of the twentieth century, the authors say, public high schools typically organized students into rigid curricular "tracks" based largely on students' past academic performance and future occupational and educational plans. During the middle of the century, however, high schools began to provide students with a choice among courses that varied in both content and academic rigor. Although the standards movement of the 1980s limited these curricular options somewhat, comprehensive curricula remained, with minority and low-income students less often completing college-prep courses. During the 1990s, say the authors, researchers who examined the associations between course-taking and student learning reported that students completing more advanced coursework learned more, regardless of their social or academic backgrounds. Based largely on this emerging research consensus favoring college-prep curriculum, in 1997 public high schools in Chicago began offering exclusively college-prep courses. To address the needs of the city's many low-performing ninth graders, schools added extra coursework in subjects in which their performance was deficient. A recent study of this reform, however, found that these approaches made little difference in student achievement. Lee and Ready hypothesize that "selection bias" may explain the divergent conclusions reached by the Chicago study and previous research. Earlier studies rarely considered the unmeasured characteristics of students who completed college-prep courses--characteristics such as motivation, access to academic supports, and better teachers--that are also positively related to student learning. Although the Chicago evaluation is only one study of one city, its findings raise the worrisome possibility that the recent push for "college-prep for all" may not generate the improvements for which researchers and policy makers had hoped. (Contains 60 endnotes.)