Social support and socioeconomic status (SES) have received considerable attention in explaining academic achievement and the achievement gap between students with ethic majority and immigrant background, and between boys and girls. Using a Structural Equation Modeling approach we examine (1) if there exist a gap in school achievements between these groups, (2) whether social support and SES is associated with achievements across these groups, (3) whether social support is associated with achievements after controlling for SES, and (4) whether achievement gaps are explained by group differences in social support and SES. Self-reported cross-sectional survey and register data from 8,574 10th graders in Norway was employed. Although we found group differences in achievements, and direct associations with social support and SES, we found no group differences in these associations. Controlling for SES and other sources of social support, teachers' support remained a significant positive influence on students' school outcomes.