Adolescents’ peer networks are integral part of their lives in school. In South Korea, where the demographics of adolescent population is rapidly changing with a growing influx of immigrants, providing opportunities for quality education for adolescents from immigrant and/or interracial families (called damnuhwa families in South Korea) has been one of the major social challenges. We examine those adolescents’ school lives with a focus on their peer networks. Using peer network data from 4575 adolescents from 11 public secondary schools, we found that adolescents’ in-degree centrality in expressive and instrumental peer networks had a significant positive association with their academic achievement. Our multilevel modeling analysis further indicated that such association did not vary by student groups (i.e., damunhwa vs. non-damunhwa adolescents). This finding suggests that peer support is crucial for student learning regardless of student background. At the same time, however, we also found that damunhwa adolescents tended to have lower levels of in-degree centrality and reciprocity, suggesting that their access to social capital via peer networks is relatively limited, compared to non-damunhwa peers. Implications for research and practice are discussed.