As part of a longitudinal study of the acquisition of reading skills, a study tested kindergarten children at the beginning and end of their kindergarten year. The children were also observed for nine full days in their classrooms. Subjects were approximately 650 children in two cohorts. Data were collected in three school districts in Illinois, of which two had half-day kindergarten programs and one a full-day program. Descriptive findings and results from multiple regression analyses reveal strong relationships between the children's Wide Range Achievement Test (WRAT) scores upon entering kindergarten and their spring scores on three measures of reading performance, the WRAT, the Chicago, and the Woodcock Reading Comprehension paragraphs. There were also substantial and significant differences among districts on these end-of-year measures. No differences were identified for time of day (A.M. versus P.M. class) or for the interaction of teacher and time of day. Among the process variables, "confirming feedback" was most frequently significant at the teacher level, and teachers in District A collectively accounted for 60% of the significant findings with respect to process variables. Findings suggest the importance of what happens in kindergarten classrooms, not merely the length of the school day. They also raise the question of whether differences between districts at the end of kindergarten will be evident in the early and middle elementary grades. (Ten tables and two figures of data are included, and 14 references are attached.) (Author/RAE)