Few studies with respect to grade retention have focused on factors that could explain differences in the learning progress of retained students. This study aims to fill this research gap by analysing the role of individual student characteristics and of classroom remedial activities that are predictive for learning progress of retained students and low-achieving students. The sample comprises students from an additional study of OECD’s Programme for International Student Assessment (PISA 2003) in Germany. N = 6339 students were promoted to the 10th grade, and 360 students were retained in the 9th grade. The results show no evidence that repeating the 9th grade improves the increase in mathematics achievement compared to the matched group of low-achieving students that have been promoted. Concerning the student characteristics the results suggest that especially students with unsatisfactory school grades gain more in mathematics if they have been promoted rather than retained. Besides that, the learning progress of the low-achieving but promoted students could be explained partly by the quality of the class-room management (monitoring activities, active learning time). Furthermore, in this group the amount of individual tutoring was predictive for learning progress in mathematics. However, in the group of retained students the amount of classroom remedial activities could not explain differences in the learning progress in mathematics. Implications of the results are discussed.