The academic penalty for gaining weight: a longitudinal, change-in-change analysis of BMI and perceived academic ability in middle school students

BACKGROUND/OBJECTIVES: Worse educational outcomes for obese children regardless of academic ability may begin early in the life course. This study tested whether an increase in children's relative weight predicted lower teacher-and child-perceived academic ability even after adjusting for standardized test scores. SUBJECTS/METHODS: Three thousand three hundred and sixty-two children participating in the Early Childhood Longitudinal Study-Kindergarten Cohort were studied longitudinally from fifth to eighth grade. Heights, weights, standardized test scores in maths and reading, and teacher and self-ratings of ability in maths and reading were measured at each wave. Longitudinal, withinchild linear regression models estimated the impact of a change in body mass index (BMI) z-score on change in normalized teacher and student ratings of ability in reading and maths, adjusting for test score. RESULTS: A change in BMI z-score from fifth to eighth grade was not independently associated with a change in standardized test scores. However, adjusting for standardized test scores, an increasing BMI z-score was associated with significant reductions in teacher's perceptions of girls' ability in reading (-0.12, 95% confidence interval (CI): -0.23, -0.03, P = 0.03) and boys' ability in math (-0.30, 95% CI: -0.43, -0.17, P < 0.001). Among children who were overweight at fifth grade and increased in BMI z-score, there were even larger reductions in teacher ratings for boys' reading ability (-0.37, 95% CI: -0.71, -0.03, P = 0.03) and in girls' self-ratings of maths ability (-0.47, 95% CI: -0.83, -0.11, P = 0.01). CONCLUSIONS: From fifth to eighth grade, increase in BMI z-score was significantly associated with worsening teacher perceptions of academic ability for both boys and girls, regardless of objectively measured ability (standardized test scores). Future research should examine potential interventions to reduce bias and promote positive school climate.