The purpose of this longitudinal study was to examine the development of spelling in a large sample (N = 503, boys: N = 219) of Greek-speaking children with (N = 41) and without (N = 462) reading difficulties. Children were initially tested in Grades 2-4 and then at five consecutive measurement points over a 3-year period, focusing on how initial reading ability, grade, and gender may moderate the rate of spelling growth. Individual growth curve modeling revealed continuous growth of spelling performance in the total sample, although the growth rate decreased over time for children first tested in Grades 3-4. Spelling growth rate was also significantly slower among children with reading difficulties between Grades 2-4 and 3-5. The two reading groups displayed similar growth rates between Grades 4 and 6. Spelling growth rates did not vary significantly with gender. Overall, our study highlights the persistence of spelling difficulties even after 6 years of systematic teaching in children with reading difficulties. The severe and persistent spelling deficits of Greek-speaking children with reading difficulties may be attributed to the rich morphological system of the Greek language, the intermediate Greek orthographic transparency (in the direction of writing), and their limited experience with print.