This study investigated the connection between language (i.e., word comprehension, reading comprehension and spelling skills) and mathematical performance. The sample consisted of grade nine students (N = 810) in 14 lower secondary schools in the Swedish speaking areas of Finland. Standardized tests for reading and writing skills, and mathematical performance were used. Based on the mathematics test the students were categorized into eight performance groups. Many students had problems in both mathematics and language performance. On the whole data level reading skills were a powerful predictor for math performance, the reading factor explained 52% of the variance in the model. Hence, the reading skills focusing on understanding of the text are important in solving mathematical tasks at the end of compulsory school. (Contains 1 figure and 2 tables.)