The study aimed to examine how the decoding, for students with decoding difficulties were affected by an intervention with reading lists. A total of 60 students participated in the study, distributed randomly into intervention groups and control groups, one cohort of primary school children and one with junior high school students. Each group included 15 students. The study was conducted as an intervention with with pre- and post-test where the students’ decoding ability were tested. The intervention included 20 occasions of 10 minutes training with reading lists by “Wendick model of intensive reading”. The study also aimed to investigate how the decoding performance of the students in the intervention appeared depending on the age of the students. Therefore, the study was conducted with students from both primary school and high school. The intervention group in primary school showed increased decoding ability compared to the control group at all tests. The results also showed that the intervention with reading lists had had a good influence on young children's development of decoding. In junior high school, the intervention group increased more, or equal, compared to the control group, and the largest increase for the intervention group was on the pseudoword reading test.