The idea of Matthew effects in reading-the widening achievement gap between good and poor readers-has attracted considerable attention in education research in the past 25 years. Despite the popularity of the topic, however, empirical studies that have analyzed the core assumption of Matthew effects in reading have produced inconsistent results. This review summarizes the empirical findings on the development of early interindividual differences in reading. We did not find strong support for the general validity of a pattern of widening achievement differences or for a pattern of decreasing achievement differences in reading. The inclusion of moderating variables, however, allowed a clearer picture to be painted. Matthew effects were more likely to occur for measures of decoding efficiency, vocabulary, and composite reading scores when the achievement tests were not affected by deficits in measurement precision. Furthermore, moderators such as the applied analytic method or the orthographic consistency of the language were of less importance for the emergence of Matthew effects in reading. An additional meta-analysis of studies reporting correlations between a baseline level and a growth parameter yielded a small, negative mean correlation (r = −.214), which again was moderated by properties of the measures. Possible explanations for the reported findings are discussed.