Background: Previous studies have shown race/ethnicity, particularly African American and/or Hispanic status, to be a predictor of overweight/obese status in children. However, these studies have failed to adjust for low socioeconomic status (SES). This study assessed whether race/ethnicity remained an independent predictor of childhood obesity when accounting for variations in SES (low-income) among communities in Massachusetts. Methods: This study was based on 2009 summarized data from 68 Massachusetts school districts with 111,799 students in grades 1, 4, 7, and 10. We studied the relationship between the rate of overweight/obese students (mean = 0.32; range = 0.10-0.46), the rate of African American and Hispanic students (mean = 0.17; range = 0.00-0.90), and the rate of low-income students (mean = 0.27; range = 0.02-0.87) in two and three dimensions. The main effect of the race/ethnicity rate, the low-income rate, and their interaction on the overweight and obese rate was investigated by multiple regression modeling. Results: Low-income was highly associated with overweight/obese status (p < 0.0001), whereas the effect of race/ethnicity (p = 0.27) and its interaction (p = 0.23) with low-income were not statistically significant. For every 1% increase in low-income, there was a 1.17% increase in overweight/obese status. This pattern was observed across all African American and Hispanic rates in the communities studied. Conclusions: Overweight/obese status was highly prevalent among Massachusetts students, varying from 10% to 46% across communities. Although there were higher rates of overweight/obese status among African American and Hispanic students, the relationship disappeared when controlling for family income. Our findings suggest low SES plays a more significant role in the nation's childhood obesity epidemic than race/ethnicity.