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Original Investigation
November 16, 2020

Effect of School-Based Body Mass Index Reporting in California Public Schools: A Randomized Clinical Trial

Author Affiliations
  • 1Berkeley Food Institute, University of California, Berkeley, Berkeley
  • 2Community Health Sciences, School of Public Health, University of California, Berkeley, Berkeley
  • 3Nutrition Policy Institute, Division of Agriculture and Natural Resources, University of California, Oakland
  • 4Division of Epidemiology and Community Health, School of Public Health, University of Minnesota, Minneapolis
  • 5Department of Epidemiology & Biostatistics, University of California, San Francisco, San Francisco
JAMA Pediatr. 2021;175(3):251-259. doi:10.1001/jamapediatrics.2020.4768
Key Points

Question  Does school-based body mass index (BMI) screening and reporting improve weight status or have unintended consequences among diverse students in grades 3 to 8?

Findings  In this cluster randomized clinical trial among 79 California schools (28 641 students participating up to 3 years), BMI reports sent to parents had no effect on BMI z scores at 1 year or 2 years of follow-up, with mixed results found on the effect of these reports on adverse outcomes.

Meaning  Although thousands of schools currently send BMI reports to parents, the practice alone has no impact on pediatric obesity and may decrease student weight satisfaction; schools should consider dedicating resources to evidence-based approaches to improve student health.


Importance  Annually, US schools screen millions of students’ body mass index (BMI) and report the results to parents, with little experimental evidence on potential benefits and harms.

Objective  To determine the impact of school-based BMI reporting on weight status and adverse outcomes (weight stigmatization and weight-related perceptions and behaviors) among a diverse student population.

Design, Setting, and Participants  Cluster randomized clinical trial. The Fit Study (2014-2017) randomized 79 California schools to BMI screening and reporting (group 1), BMI screening only (group 2), or control (no BMI screening or reporting [group 3]) in grades 3 to 8. The setting was California elementary and middle schools. Students in grades 3 to 7 at baseline participated for up to 3 years. A modified intent-to-treat protocol was used. Data analysis was conducted from April 13, 2017, to March 26, 2020.

Interventions  School staff assessed BMI each spring among students in groups 1 and 2. Parents of students in group 1 were sent a BMI report each fall for up to 2 years.

Main Outcomes and Measures  Changes in BMI z score and in adverse outcomes (based on surveys conducted each fall among students in grades 4 to 8) from baseline to 1 and 2 years of follow-up.

Results  A total of 28 641 students (14 645 [51.1%] male) in grades 3 to 7 at baseline participated in the study for up to 3 years. Among 6534 of 16 622 students with a baseline BMI in the 85th percentile or higher (39.3%), BMI reporting had no effect on BMI z score change (−0.003; 95% CI, −0.02 to 0.01 at 1 year and 0.01; 95% CI, −0.02 to 0.03 at 2 years). Weight dissatisfaction increased more among students having BMI screened at school (8694 students in groups 1 and 2) than among control participants (5674 students in group 3). Results of the effect of BMI reporting on other adverse outcomes were mixed: compared with the control (group 3), among students weighed at school (groups 1 and 2), weight satisfaction declined more after 2 years (−0.11; 95% CI, −0.18 to −0.05), and peer weight talk increased more after 1 year (0.05; 95% CI, 0.01-0.09); however, concerning weight control behaviors declined more after 1 year (−0.06; 95% CI, −0.10 to −0.02).

Conclusions and Relevance  Body mass index reports alone do not improve children’s weight status and may decrease weight satisfaction. To improve student health, schools should consider investing resources in evidence-based interventions.

Trial Registration  ClinicalTrials.gov Identifier: NCT02088086

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