Children residing in McLean County, Kentucky, and attending grades three through six who either had or had not attended kindergarten were compared in terms of academic aptitude, total reading, language expression, and math application scores on the Comprehensive Test of Basic Skills (CTBS). It was found that students who had attended kindergarten scored higher in academic aptitude at all four grade levels tested than students who had not attended kindergarten. These differences were significant at grades three, four, and six. When academic aptitude was built into analyses of achievement measures as a covariate to statistically equate groups on ability, children who had attended kindergarten were found to outscore children who had not attended kindergarten in all three achievement measures at every grade level tested. However, differences between groups were large enough to produce statistical significance in only one of the 12 comparisons--language expression at the third grade level. It was concluded that McLean students who attended kindergarten tend to outperform students not attending kindergarten when differences in academic ability are controlled. (Comparisons also were made between each of the two groups and national norms.) (Author/RH)