To evaluate classroom processes for teaching basic reading and mathematics, particularly individualized instruction in the context of compensatory education, a model of classroom processes was applied to disadvantaged children from 400 schools, grades one and three. The model specified that criterion performance is a function of initial student performance and four classroom processes: opportunity, motivators, instructional events, and structure. Criterion performance was measured by achievement gains on the Comprehensive Test of Basic Skills. A list of observable and measurable variables for each process was identified. Opportunity was the most powerful predictor of achievement gain. The most important findings for policy makers are the lack of clear evidence regarding the superiority of individualized instruction for compensatory education, and the insignificant relationship between extent of pull-out instruction and achievement. The strongest predictor of achievement gains, opportunity, refers to the degree of overlap between what was taught in a specific classroom and end-of-year achievement test content, as estimated by the teacher and by curriculum content analysts. The data imply that what is taught is more important than how. The appendix includes a rationale for the four processes and their respective variables, commonality analysis results, and correlations with gain for each predictor variable. (CP)