Using a sample of 9,631 students in 789 U.S. high schools with three waves of data from the National Education Longitudinal Study of 1988, the study presented here was an extension of an earlier study that found positive effects for practices that are consistent with the restructuring movement on learning in the first two years of high school and on the equitable distribution of learning by social class. The current study identified the characteristics of high school organization that are positively related to learning in mathematics and science and to equity during the first and last two years of high school and investigated whether such organizational factors explain the results of the earlier study. It found that although students learn somewhat less in the last two years than in the first two years, several features of the social and academic organization of high schools are strongly associated with learning in both periods.