In school settings, students' mindset about intelligence (i.e., fixed versus growth mindset) and their sense of belonging to school (SBS) have both been shown to predict academic attainment. However, these constructs have rarely been examined together although both were found to be impacted by students' socioeconomic status (SES). Across the literature, findings are inconsistent concerning this moderating effect of SES. In the present preregistered study, we used data from the French sample of the Programme for International Student Assessment 2018 (PISA; N = 6308) to examine whether growth mindset positively predicted SBS and whether this association was moderated by students' SES. Results showed that growth mindset was positively associated with SBS. On the confirmatory linear regression analyses, we found no moderation effect of any of the SES indicators on the association between growth mindset and SBS. However, pre-registered supplementary multigroup analyses showed descriptively that this association was stronger for high than for low SES students and notably when SES indicators concerned family financial resources. Limitations of this research and perspectives for future studies are discussed, with a focus on why the literature should care about the different meanings and consequences of SES indicators.