The era of "high stakes" testing in older grades has contributed to higher achievement expectations in the preschool years. Early childhood is a significant period in the development of the whole child. The skills children build in kindergarten are fundamental to learning success. The purpose of this study was to examine differences in later academic achievement between groups of students based on their categories of Developmental Indicators Assessment of Learning-Revised (DIAL-R) score when entering kindergarten. This study investigated whether there were statistically significant differences in later academic performance through twelfth grade between groups of private school students based on a pre-kindergarten readiness assessment (DIAL-R). The sample consisted of 265 math students and 263 reading students who attended a private school, located in middle Tennessee, from kindergarten through twelfth grade. Questions one and two investigated, using repeated-measures analysis of variance, if there were a significant difference in TerraNova mathematics and reading scores of second, third, fourth, fifth, and sixth grade students based on their scores of "Potential Problem," "OK," or "Potential Advanced" on the DIAL-R in kindergarten. A between-subjects effect in mathematics was found to be significant. In addition, a between-subjects effect in reading was found to be significant. This suggests a significant difference between the mean TerraNova mathematics and reading scores of students categorized as "OK" versus "Potential Advanced" on the DIAL-R in kindergarten. The results for the PLAN mathematics and reading ANOVAs indicated a significant category effect. These results suggest that there is a significant difference in PLAN mathematics and reading scores of tenth grade students based on their group of "OK" or "Potential Advanced" on the DIAL-R in kindergarten. The mathematics and reading results for the ACT ANOVAs indicated a significant category effect. These findings suggest that there is a significant difference in ACT mathematics and reading scores of twelfth grade students based on their group of "OK" or "Potential Advanced" on the DIAL-R in kindergarten. This study strongly suggests DIAL-R is useful as a diagnostic tool in identifying later academic performance in mathematics and reading between groups of private school students. (author abstract)