Declining achievement in various core subjects has led to a debate on strategies to enhance student achievement. Identifying factors in the school environment that affect student performance in science, are therefore, of vital importance. The aim of this study is to identify school-level factors that are associated with eight-grade students' achievement in science based on results from TIMSS (Trends in Intrrnational Mathematics and Science Study) 2003 and 2007. Because the TIMSS data includes school-level factors at two different time points, we expected to find factors that influence science performance by Swedish and Norwegian students. Multilevel analysis was used, and this framework allowed us to account for the influence of the students' home backgrounds. After controlling for student background, our results show that there are only a few school-level factors that are associated with student achievement in science, and the influence of these factors differ between Sweden and Norway.