This article reports findings obtained from a large-scale national study (299 schools; 2761 students) that examined academic achievements of immigrants in Israeli schools. It focused on two distinct groups of immigrant students--those from the former USSR and from Ethiopia, in two subject areas--mathematics and academic language (Hebrew), and in three grade levels--5, 9 and 11. The scores of the immigrant students and those of a parallel group of native-borns were compared and analyzed. The findings demonstrate differences in achievements between the groups. The scores also demonstrate that immigrants require a substantial number of years to reach achievement levels similar to those of students who were born in Israel in academic subjects, specifically, 5-7, 9 or 11 years in mathematics, and 5-7, 8 or 11 years in academic Hebrew, depending on the grade levels and the groups. The study discusses the implications of using large-scale evaluation of educational achievement for educational policy and evaluation designs.