Same-year and same-grade comparisons were made of a matched sample of students who had been retained in kindergarten for a second year and who had been promoted after 1 year from kindergarten within the Pasco County (Florida) School System. Retained subjects (n=34) consisted of kindergarten students enrolled in the system's developmental kindergartens during the 1984-85 academic year. The developmental program constitutes a component of the state-legislated Primary Education Program for at-risk students. A matched group of non-retained subjects (n=33) was used as a control. Longitudinal performance in first, second, and third grades was studied using standardized test scores in reading and mathematics, and students' performances were compared using multivariate analyses and Bonferroni comparisons. For both the same-year and the same-grade comparisons, significant group effects were found in reading; however, significant group effects were found in mathematics only for same-grade comparisons. Significant interaction effects were found for both disciplines. Results underscore the possibility that an individualized education plan during the retained year could be partly responsible for the improvement in performance for retainees. Five data tables and four graphs are included. (Author/TJH)