This study examined the hypothesis that children who had participated in a full-day kindergarten program would not show a significantly higher academic achievement in first grade as measured by the standardized portfolio assessment than children who participated in a half-day program. The study compared four portfolio assessment scores of two groups of first grade students in the East Brunswick Public School District (New Jersey). The first group consisted of 16 children who participated in a full-day kindergarten program, and the second group consisted of 61 children who participated in a half-day kindergarten program. Results showed that the full-day kindergarten sample scores were higher in all areas than the half-day kindergarten sample, however, only significantly higher in one area--the Developmental Spelling Assessment subtest of the standardized portfolio. Findings suggest support for the hypothesis. (Contains 5 tables of data, 4 footnotes, and 31 references; related research and 10 pages of scores are appended.) (Author/CR)