Background: The current study investigates school contextual effects on students' academic self-concept and achievement, that is, peer socioeconomic effect and big-fish-little-pond effect (BFLPE), in four Nordic education systems (i.e., Denmark, Finland, Norway and Sweden) and selected Chinese education systems (Hong Kong and Beijing-Shanghai-Jiangsu-Zhejiang). The two school contextual effects are studied simultaneously to negate the confounding effects of student and school socioeconomic status (SES), academic self-concept and academic achievement. The study focuses on the following research questions: (1) Are there differences in the between-school variation in school SES composition, academic self-concept and reading literacy across the Nordic and selected Chinese education systems? (2) What are the sizes of peer SES and BFLPE in the Nordic and Chinese education systems? and (3) Are there any differences that can be observed between the 2000 and 2018 data for the Programme for International Student Assessment (PISA) in the first two questions for Denmark, Finland, Norway and Sweden and Hong Kong? Methods: Using PISA 2000 and 2018 data from Denmark, Finland, Norway, Sweden, Hong Kong and Beijing-Shanghai-Jiangsu-Zhejiang (in 2018 only), a multiple-group two-level structural equation modelling was applied to estimate the school contextual effect. Results: The current study indicated that school academic and socioeconomic segregation intensified over the two decades in most of the studied countries. This finding lays the groundwork for understanding the two schools' contextual effects. School SES compositions positively affected students' academic achievement, while average school achievement negatively affected students' academic self-concept. Given that students' academic and socioeconomic composition has become more homogeneous within schools, the contextual effects were more pronounced. However, variations across diverse education systems were also notable. Conclusions