This study, comparing the academic achievement levels of the students with different primary school entrance age, is in survey model. 60 students, at the second grade of a primary school centrally located in Tokat province in the year the study was conducted and were 60-66 and 73-84 months old when entered the primary school, were selected with the random sampling technique. Data was obtained through the tests in Turkish, Mathematics, and Social Studies subjects applied by the researcher, and from the second year end-of-first term grades. The averages of test scores and end-of-first term grades were analyzed using t-test. In the analysis, while there was a significant difference at a level of 0.01 between test scores and first term average grade points according to the school entrance age, no difference was found in terms of gender. It was concluded from the analysis that the children who started school when 73-84 months old were more successful than those 60-66 months old. Therefore, it could be suggested that the children should be directed to pre-school education at 60-66 months age range, and more research on the achievement of children started school at the age of five is needed to be conducted.