The aim of this study was to assess sedentary behavior during school recess in Brazilian boys and girls. The study included 455 students (233 boys and 222 girls), aged 8 to 17 years, enrolled in a public school in the city of Londrina, Brazil. All data was collected using questionnaires. Logistic regression with odds ratio and confidence interval (95%) was used to measure the relationship between sedentary behavior and sex, age, weight, screen time, and economic status. There was a high prevalence (40.7%) of sedentary behavior in this sample, with girls (aged 8 to 17 years) more likely than boys (54.5% vs. 27.5%, respectively) and older students (13–17 years) more likely than younger students (8–12 years) to engage in sedentary behavior (49.6% vs. 30.1%, respectively). These findings, and their broad implications for health and for interventions to increase physical activity, are discussed in light of past literature.