It examines whether such proficiency can be explained by reading proficiency in Norwegian as their first language (L1). The analysis uses data from two national reading tests, comprising a large sample of 16-year-old students (N=10,331), and it is the first time reading across these languages has been investigated at this level. The results show a significant and meaningful relationship between students' reading proficiency in the two languages. The results also reveal marked reading differences in reading proficiency in the two languages among poor readers. [ABSTRACT FROM AUTHOR]