In this study, kindergarteners and first-to-third graders were assessed in Korean literacy (word reading, word reading fluency, spelling, and reading comprehension) and cognitive skills (phonological, orthographic, and morphological awareness, as well as naming speed, left-right reversal, and vocabulary). This study aimed to compare the literacy skills between poor readers and all children in each grade, as well as to determine the rate of cognitive deficits that appear in poor readers. We found that the average score of poor readers was more than a year below that of all children on all literacy tests. In particular, the proportion of children who could not read CV and CVC Gulja (written syllable) in the test immediately prior to entering elementary school was 48% and 95%, respectively, in the poor readers, whereas it was 7% and 24%, respectively, in all children, demonstrating a significant difference between the two groups. More than 30% of poor readers in the second and third grades had deficits in all types of cognitive skills except left-right reversal. The findings of this study suggest that it is necessary to identify and intensively train children who have not mastered how to read CV and CVC Gulja in the early first grade.