Despite the multiple meta-analyses documenting the association between socioeconomic status (SES) and achievement, none have examined this question outside of English-speaking industrialized countries. This study is the first meta-analytic effort, to the best of our knowledge, to focus on developing countries. Based on 49 empirical studies representing 38 countries, and a sample of 2,828,216 school-age students (grades K-12) published between 1990 and 2017, we found an overall weak relation between SES and academic outcomes. Results for attainment outcomes were stronger than achievement outcomes, and the effect size was stronger in more economically developed countries. The SES-academic outcome relation was further moderated by grade level and gender. There were no differences in the strength of the relation by specific SES measures of income/consumption, education, and wealth/home resources. Our results provide evidence that educational inequalities are wider in higher income countries, creating a serious challenge for developing countries as they expand school access.