Experts widely consider decoding and fluency as the basis of reading comprehension, while at the same time consistently documenting problems in these areas as major characteristics of students with learning disabilities. However, scholars have developed most of the relevant research within phonologically deep languages, wherein decoding problems appear to be especially prominent. Furthermore, most of the available data refer to elementary-age students. The goal of this study was to investigate reading comprehension in Greek, a language that is less transparent than English. Specifically, the aims of this cross-sectional study were (a) to provide a qualitative analysis of reading comprehension errors in narrative and expository texts made by students across 9 grades and (b) to predict specific reading comprehension problems from decoding and fluency skills. Participants were 1,070 elementary and secondary students from the 1st through the 9th grades whom researchers assessed using a newly developed detection test of reading difficulties. We discuss the results of frequency and regression analyses in the framework of understanding the role that decoding and fluency play in reading comprehension.