Childhood overweight and obesity have increased over the past decades1 with children residing in rural areas and those of ethnic minority status being disproportionally impacted.2 Childhood overweight and obesity have been associated with negative physical health outcomes, decreased quality of life, and psychological distress.3,4 In response, childhood overweight and obesity have been identified as a pressing public health problem, leading to calls for increased efforts to treat and prevent childhood obesity.3,5 School-based settings may be an effective location to conduct prevention and intervention activities. However, many schools, under pressure to increase academic achievement, have decreased or eliminated recess and physical education6 and may hesitate to spend instructional time on nutrition education or interventions. Research is warranted to investigate potential associations among childhood overweight and obesity, physical activity, and academic achievement to address constraints in schools. Adiposity and Academic Achievement Different methods have been used to assess adiposity, including self-reported or directly-measured height and weight, used to calculate body mass index (BMI), or percentage body fat, and academic achievement, including self-reported grade point average (GPA), teacher-assigned GPA, or standardized test scores. Research findings have been equivocal concerning the association between adiposity and academic achievement and these differing methodologies may account for the divergent findings. An inverse association has been found in studies utilizing BMI calculated with self-reported data and academic achievement; however, this association has been weak or inconsistent across demographic groups. For example, Sabia7 found a negative body weight-achievement relation for white girls, but not for nonwhite girls or boys of any ethnic group. Results were statistically significant, but a 50–60 pound (22.7 to 27.3 kg) weight increase was associated with only a 0.2 GPA reduction. Reliance on self-reported data for BMI and academic achievement is a limitation. Children and adolescents can be inaccurate reporters of BMI8 and academic performance9 and method bias also may limit self-report. In support, Huang et al. found different results in the same sample, depending on measurement of achievement. Overweight status was inversely related to achievement in middle school children, but only for self-reported grades. There was no BMI-achievement relation for teacher-reported grades.10 Recognizing these limitations, researchers have used standardized measurements of weight and achievement and found negative and significant, yet weak, correlations. Obese status was related to lower test scores in kindergarten in a national sample, but the correlation weakened or disappeared when SES and other variables were controlled.11 Datar and Sturm12 examined change in weight from kindergarten to third grade with three groups: never overweight, became overweight, and always overweight. Girls who became overweight had significantly lower test scores than girls who had never been overweight, although parental income and education were more strongly related to achievement than weight status change. There were no differences between girls who had always been overweight and those who had never been overweight, or any significant results for boys.12 These results did not support a strong inverse association between weight and academic achievement. Any correlation between adiposity and academic achievement may be attributed to mediator variables, such as weight bias or teasing. One study examined weight and academic achievement in a middle school sample using teacher-assigned GPA and a standardized reading assessment. Lower achievement was found for teacher-assigned grades, but not for the reading test.13 Overweight students may have been assigned lower grades by teachers due to weight bias; in support of this possibility, researchers have documented weight bias in educators, e.g., negative beliefs about obese children.3 Concerning negative peer interactions, Krukowski et al. found a weak, yet significant relationship between BMI and parent-reported grades in girls, but not boys. When weight-based teasing was added to the model, the BMI-grade association disappeared, indicating that weight-bias teasing functioned as a mediator variable.14 Physical Activity Research on the relation between physical activity and academic achievement has also yielded inconsistent findings across studies. Also, similar to the adiposity-achievement research, studies on the relationship between physical activity and academic achievement have used different methods to assess both variables. Some studies with self-reported physical activity have reported a positive association. For instance, Stevens et al.15 investigated parent- and school-reported physical activity and test scores in a national sample and found a small, yet significant correlations (r = 0.11 to 0.16) between parent-reported physical activity and test performance, but not school-based physical education (r = 0.01 to 0.04). Conversely, other studies found weak negative associations (r = −0.03 to −0.07) between physical activity and achievement.16,17 These equivocal findings may be related to the questionable reliability and validity of self- and parent-report for children. Developmental differences between adults and children, including children’s different concepts of time; sensitivity to socially desirable responding; and difficulty separating behavioral intentions and actual behavior, may decrease the psychometric properties of self-report.18 In support, a review of assessment methods revealed that self- and parent-reports overestimated physical activity compared to accelerometry and heart rate monitoring.18 Randomized controlled trials (RCT) designed to increase physical activity during school have examined changes in academic achievement. Some studies have found that physical activity interventions in schools do not lead to improved academic achievement.19–21 Conversely, one RCT found greater achievement gains for intervention schools than control schools across three years.22 Overall, evidence suggests that time spent in physical activity does not result in academic decline and may be associated with gains. Several mechanisms for the physical activity-achievement link have been proposed. For example, the executive functioning hypothesis posits that physical activity improves executive functioning, as well as other neuropsychological processes, such as processing speed and visual-spatial processing. These improved functions enable children to develop behaviors necessary for academic achievement, such as planning, metacognition, attention, and behavioral self-control.23 Other psychological constructs, such as depression and self-esteem, may also serve as mediators of the physical activity-achievement association. However, Tomporowski et al. recently noted that there is no strong theory underlying any association between exercise and cognition.23 Current Study Recent studies have reported that the connection between childhood overweight and obesity and reduced achievement has been unequivocally supported in the literature (e.g., Cho et al.24). However, the evidence for this association is mixed and leans towards no meaningful association between adiposity and academic achievement. Studies that found a stronger inverse relation generally relied on self-report. Those with objective assessment have found either weak correlations or that significant correlations are diminished when other variables, such as SES, are statistically controlled. Nonetheless, the hypothesis that being overweight or obese is associated strongly with diminished academic achievement persists. Similarly, studies of physical activity and academic achievement are limited by methodological weaknesses, such as reliance on self-report and different operational definitions of physical activity, and results are mixed. A recent review of the literature concluded that research using accelerometry to measure physical activity is needed to test the hypothesis that higher levels of physical activity are associated with higher academic achievement.25 In conclusion, the associations among adiposity, physical activity and academic achievement in children are unclear due to conflicting findings and differences in methodological rigor. The primary aims of this cross-sectional study were to test the following two hypotheses in a relatively large sample of elementary school students using objective measurement of body weight, academic achievement, and physical activity: 1) there is a negative correlation between adiposity (defined by body mass index percentile and percent body fat) and academic achievement and 2) physical activity is positively correlated with academic achievement.