A study was done of the effects of school practices and curriculum offerings on eighth graders nationally. The study used data from the National Education Longitudinal Study of 1988, a survey of 24,600 eighth graders in 1,035 public and independent schools as well as the Hopkins Enhancement Survey of school practices. The results reveal that in many schools students are not offered real challenges in advanced academic courses and have few opportunities to experience rich instructional approaches that develop higher level skills. However, when these opportunities to learn are extended, students of all levels of ability benefit in higher achievement and more positive attitudes. Other findings include the following: (1) students in homogeneously grouped algebra classes, regardless of the ability level of the class, perform better than do students in heterogeneous algebra classes; (2) heterogeneous grouping in English classes does not disadvantage high-, average-, or low-ability students; (3) opportunities to learn through frequent experiences with high level instructional approaches influence eighth graders' achievements and attitudes; and (4) generally, the results suggest the need for greater equity in access to advanced curriculum offerings and challenging instructional approaches for all students. Included are 11 tables, 1 figure, 2 appendixes with 2 tables, and 30 references. (JB)