This article aims to evaluate a whole-class reading program (LARS) and its effects on decoding, reading comprehension, and language abilities of L1 and L2 German second graders. The program consisted of teacher training and differentiated reading materials offered adapted to the needs of both L1 and L2 learners. The materials were divided into four different reading levels. For the evaluation, a pre-posttest design with a comparison group was used. Decoding, reading comprehension, and language abilities of all students (n=377) were assessed before and after the implementation of the program. 159 students received reading instruction twice a week with the LARS program during regular school hours for a period of seven months. 218 students received conventional reading instruction without special materials (e.g. no differentiated materials) provided by the research team. The results indicate that the development of reading comprehension and expressive vocabulary (trained words) was significantly improved by the program.