Body Mass Index (BMI) Measurement in Schools

BMI Measurement in Schools Banner

Overview

There are two types of BMI measurement programs and each serves a specific purpose.

  1. Surveillance: To identify the percent of students in the school or school district who are underweight, healthy weight, overweight or obese. These data are typically anonymous and can be used to identify trends over time or monitor the outcomes of a school policy or practice aimed to improve student health. This is not to inform parents of their child’s weight status.
  2. Screening: To provide parents with information on whether their child is underweight, healthy weight, overweight or obese.

CDC does not make a recommendation for or against BMI measurement programs in schools.1 However, it does recommend that a school have the following in place before it launches a BMI measurement program:

  • A safe and supportive environment for students of all body sizes.
  • A comprehensive set of strategies to prevent and reduce obesity. The CDC’s School Health Guidelines to Promote Healthy Eating and Physical Activity can serve as the foundation for developing, implementing, and evaluating school-based healthy eating and physical activity policies and practices for students.
  • A series of safeguards that address the primary concerns raised about such programs.
What evidence is available on the effectiveness of school BMI measurement programs?

To date, there is not enough evidence for scientists to conclude whether school-based BMI measurement programs are effective at preventing or reducing childhood obesity or whether they cause harm, by either increasing the stigma attached to obesity or increasing pressures to engage in unsafe weight control behaviors 1-3 To minimize the risk for potential negative consequences, screening programs should follow safeguards. 1-3

Many-researchers and public health professionals believe that efforts to measure BMI in schools have potential benefits and should be studied more closely because

  • Obesity is highly prevalent and has a significant impact on health.4
  • BMI is an acceptable measure of weight status.5
  • Many school districts already require health screenings for other conditions.6
  • The majority of school-aged youth in the US are enrolled in schools.7

Before implementing these programs, decision makers need to consider the costs involved, potential negative consequences for students, and existing school-based strategies to support healthy weight-related behaviors and prevent weight-based bullying.

Safeguards

Safeguards are an essential part of a BMI measurement program. They help to ensure respect for student privacy and confidentiality, protect students from potential harm, and increase the likelihood that the program will have a positive impact on promoting a healthy weight. Safeguards 1–8 are relevant to both screening and surveillance programs. In schools that screen students’ BMI, additional safeguards (Safeguards 9 and 10) are needed to ensure that parents have what they need to make informed decisions and take follow-up actions.

All of the safeguards are from the same source: Nihiser AJ, Lee SM, Wechsler H, McKenna M, Odom E, Reinold C, Thompson D, Grummer-Strawn L. Body Mass Index Measurement in Schools. Journal of School Health. 2007; 77:651–671.External

Safeguard 1. Introduce the program to parents, guardians, students, and school staff; ensure that there is an appropriate process in place for obtaining parental consent for measuring students’ height and weight.

To help minimize negative response from the public, programs need to involve parents or guardians early in the planning stages.1–2 Before the program begins

  • All parents should receive a clear description of the program to minimize confusion and anxiety.
  • Communications with parents should focus on the health implications of obesity, overweight, and underweight, and make it clear that the school will be measuring weight out of concern for a student’s health, not their appearance or a desire to criticize parenting practices.3–4
  • Schools should assure parents and students that the screening results will remain confidential.
  • In addition, students and school staff should be informed of the purposes and logistics of height and weight measurement, as well as the school’s policy on sharing results.

Parents must be given the option of declining permission to measure their child’s BMI.1–2 Some programs use passive parental consent; that is, all students have their BMI measured unless parents send a written refusal. For example, at the beginning of each school year, school districts can inform parents about the school health program and the screenings that are conducted in each grade. Parents can choose not to have their child screened; otherwise, all students are measured. Alternatively a school district can require active consent from both parents and students; only students who signed the consent form and whose parents have submitted a signed consent form would be screened.

References

  1. Byrd S. Dealing with controversy: the lessons of implementing BMI screenings. NASN Newsletter. 2003;18(1):18-19.
  2. Johnson A, Ziolkowski GA. School–based body mass index screening program. Nutr Today. 2006;41(6):274-279.
  3. American Academy of Pediatrics. Policy statement: prevention of pediatric overweight and obesity. Pediatrics. 2003;112(2):424-430.
  4. Society for Nutrition Education. Guidelines for childhood obesity prevention programs: promoting healthy weight in children. J Nutr Educ Behav. 2003;35(1):1-4.
Safeguard 2. Ensure that staff members who measure height and weight have the appropriate expertise and training to obtain accurate and reliable results and minimize the potential for stigmatization.

Accurate measurements correspond to a child’s actual height and weight.1  

Reliable measurements produce consistent results when they are repeated.1

Measurements are more likely to be accurate and reliable when they are conducted by trained professionals, such as school nurses.2–3 Unfortunately, many schools do not have full-time nurses on campus,4 and many school nurses feel that they cannot add another responsibility to their workload.5 Staff members involved in a BMI measurement program need appropriate technical training from people who are experienced in conducting height and weight measurements and calculating and interpreting BMI results.6

Conducting repetitive tasks, such as measuring height and weight, can be tedious and may lead an individual to become careless and fail to consistently follow measurement protocols. Quality control checks can be implemented through random visits at measurement sites to oversee the performance of the staff measuring students’ height and weight.

For example, staff members need to ensure that

  • Each student takes off his or her shoes and jacket or other heavy clothing items and removes all items from his or her pockets before being weighed7
  • Hair styles do not interfere with an accurate measurement of height7

Each measurement should be taken twice and the student should be repositioned prior to each measurement.1 If the two measurements do not agree within one-fourth of a pound for weight (0.25 lb) or one-fourth of an inch for height (0.25”), then two additional measures should be taken until there is agreement.1,6 Height errors, in particular, reduce the validity of BMI.1

Staff also need training to measure height and weight in a sensitive and caring manner. This training should

  • Address procedures to maintain student privacy during measurement8
  • Increase awareness of groups at increased risk of stigmatization
  • Provide information about body size acceptance and the dangers of unhealthy weight control practices
  • Help staff identify signs of student problems related to weight or body image (e.g., eating disorders)

Staff should be prepared to respond to questions or comments by students. For example, if a student makes a negative comment about his or her own weight, staff members need to be able to respond with supportive statements such as, “Kids’ bodies come in lots of different sizes and shapes. If other kids are teasing you about your body, let’s talk and see what we can do about it.”9 Staff members also need to know how to respond to questions about what the school will do with the measurement results and referrals.

Resources that can assist with training on height and weight measurement and with avoiding weight stigmatization include

  1. CDC’s Division of Nutrition, Physical Activity, and Obesity Growth Chart Training
  2. Health Resources and Services Administration’s Maternal and Child Health BureauExternal
  3. The Center on Weight and Health’s Guidelines for Collecting Heights and Weights on Children and Adolescents in School SettingsCdc-pdf[pdf – 336 KB]External
  4. Rudd Center Resources for Schools and EducatorsExternal

References

  1. US Department of Health and Human Services, Health Research and Services Administration, Maternal and Child Health Bureau. Growth charts training: accurate weighing and measuring. U.S. Department of Health and Human Services; 2006. Available at: http://depts.washington.edu/growth/External.
  2. American Academy of Pediatrics, Committee on School Health. The role of the school nurse in providing school health services. Pediatrics. 2001;108(5):1231–1232.
  3. Ikeda JP, Crawford PB, Woodward–Lopez G. BMI screening in schools: helpful or harmful. Health Educ Res. 2006;21(6):761–769.
  4. Brener ND, Wheeler L, Wolfe LC, Vernon–Smiley M, Caldart–Olson L. Health services: results from the School Health Policies and Programs Study 2006. J Sch Health. 2007;77(8):464–485.
  5. University of Arkansas for Medical Sciences, College of Public Health. Year two evaluation: Arkansas Act 1220 of 2003 to combat childhood obesity. University of Arkansas for Medical Sciences; 2006. Available at: www.uams.edu/coph/reports/Act1220Eval.pdfCdc-pdfExternal.
  6. Gance-Cleveland B, Bushmiaer M. Arkansas school nurses’ role in statewide assessment of body mass index to screen for overweight children and adolescents. J Sch Nurs. 2005;21(2):64–69.
  7. Ikeda JP, Crawford PB. Guidelines for collecting heights and weights on children and adolescents in the school setting. University of California Berkeley, Center for Weight and Health; 2005. Available at: http://cwh.berkeley.edu/sites/greeneventsguide.org.cwh/files/primary_pdfs/bw_weighing_0.pdfCdc-pdfExternal.
  8. Haller EC, Petersmarck K, Warber JP, editors. The role of Michigan schools in promoting healthy weight. Lansing, MI: Michigan Department of Education; 2001. Available at: http://www.michigan.gov/documents/healthyweight_13649_7.pdfCdc-pdfExternal.
  9. Crawford PB, Woodward–Lopez G, Ikeda JP. Weighing the risks and benefits of BMI reporting in the school setting. Center for Weight and Health; 2006. Available at: http://cwh.berkeley.edu/sites/default/files/primary_pdfs/BMI_report_cards_0.pdfCdc-pdfExternal.
Safeguard 3. Ensure that the setting for data collection is private.

Height and weight measurements must not be conducted within sight or hearing distance of other students. The trained staff member conducting the measurement should be the only person to see the results and should not announce them out loud.1 To maintain anonymity when collecting data for surveillance purposes, school staff should remove identifying information, including the student’s name, from the data collection form as soon as record keeping is complete and prior to calculating BMI and aggregating and analyzing the data.2

References

  1. Haller EC, Petersmarck K, Warber JP, editors. The role of Michigan schools in promoting healthy weight. Lansing, MI: Michigan Department of Education; 2001. Available at: http://www.michigan.gov/documents/healthyweight_13649_7.pdfCdc-pdfExternal.
  2. Rao JN, Routh K, Denley J. Measuring the prevalence of childhood obesity: a minimalist approach may be the best option. Child Care Health Dev. 2006;32(2):245–252.

Safeguard 4. Use equipment that can accurately and reliably measure height and weight.

The preferred equipment to assess students’ weight is an electronic or beam balance scale that is properly calibrated to the nearest one-fourth pound according to the manufacturer’s directions.1 Spring balance scales, such as bathroom scales, are not sufficiently accurate. The preferred equipment to assess height is a stadiometer, a wall-mounted or portable unit solely designed to measure height to the nearest one-eighth inch.1 The stadiometer should include a vertical board, metric tape, and horizontal headpiece that slides down to measure height. All equipment should be maintained and calibrated regularly.1

References

  1. US Department of Health and Human Services, Health Research and Services Administration, Maternal and Child Health Bureau. Growth charts training: accurate weighing and measuring. US Department of Health and Human Services; 2006. Available at: depts.washington.edu/growth/External.
Safeguard 5. Ensure that the BMI number is calculated and interpreted correctly.

The English formula for calculating BMI is

{Weight (lb) ÷ [Height (in)]2} × 703

Schools should establish the BMI-for-age percentile using the CDC growth charts.1 Staff must collect the student’s correct age in years and months as well as their gender to properly plot the BMI on the CDC growth charts. Schools conducting BMI screening programs should refer youth categorized as underweight, overweight, or obese to a medical care provider for diagnosis and possible weight management counseling.

Resource

CDC’s About BMI for Children and Teens

Reference

  1. Kuczmarski RJ, Ogden CL, Grummer–Strawn LM, et al. CDC growth charts: United States. Adv Data. 2000;(314):1–28.

Safeguard 6. Develop efficient data collection procedures.

To facilitate efficient and accurate data collection, BMI measurement programs should coordinate data collection times with school administrators and employ a sufficient number of staff members to minimize disruptions to class time.

CDC’s BMI Tool for Schools is an excel spreadsheet that can compute up to 2000 BMI and BMI percentiles and provide a summary of students’ BMI-for-age categories and graphs for the prevalence of overweight and obesity. Software can substantially reduce the time it takes staff to conduct screenings. Other software may be available that can both aggregate the data and produce health report cards.

Safeguard 7. Do not use the actual BMI-for-age percentiles of the students as a basis for evaluating student or teacher performance (e.g., in physical education or health education class).

Many factors beyond physical education and health education courses influence a student’s weight, so it is not appropriate to hold students or teachers accountable for changes in BMI percentiles. Using BMI results to evaluate performance might heighten attention to weight and increase stigmatization and harmful weight-related behaviors.

Knowledge, skills, and changes in dietary, physical activity, and sedentary behaviors are more appropriate as performance measures.

Safeguard 8. Evaluate the BMI measurement program by assessing the process, intended outcomes, and unintended consequences of the program.

Data should be collected on concerns about the program, such as stigmatization, cost, parental responses, and displacement of other health–related initiatives. Schools can use the evaluation results to guide improvements to their program. The results should be shared with key stakeholders, parents, the community, school administrators, and policy makers in order to inform their decisions about school-based BMI measurement.

Resource

CDC Program Evaluation

Resource

CDC Program Evaluation

Safeguard 9. Ensure that resources are available for safe and effective follow-up.

BMI screening programs are not intended to diagnose weight status. Schools should refer students who need follow-up to appropriate local medical care providers.

Actions to initiate a screening program

Schools

  • Work with the local medical community to ensure that adequate diagnostic and treatment services are available, staffed by employees with appropriate training, and accessible to all students, including those with low family incomes or without insurance.
  • Identify school- or community-based health promotion programs that encourage physical activity and healthy eating.

School Nurses

  • Be educated, trained, and equipped with the appropriate resources to respond to parents requesting guidance.1
  • A valuable resource during the follow-up period, school nurses can provide parents with a clear explanation of the results and health risks associated with obesity, develop an action plan for behavior change, and connect the family to medical care in the community.1

School Health Personnel

  • Establish systematic processes and criteria for referring students to external medical care providers.2
  • Refer students with signs of underweight, overweight, obesity, disordered eating, or other diet-related health conditions (e.g., sudden weight loss, eating disorders) to a local medical care provider for diagnosis and, if needed, establish a management or treatment plans. For example, students classified as obese or overweight after BMI screening require further medical examination to determine whether the student in fact has excess body fat or other conditions related to obesity (e.g., diabetes or prediabetes, high blood cholesterol or  triglyceride levels, early pubertal maturation).3–5

School Staff

  • Receive guidance on how to recognize early signs of health risks that require urgent attention such as hunger or disordered eating. If a school staff member suspects a student to have these risk behaviors, staff should confidentially refer these students to school health or mental health personnel.

Schools can play an important role in developing and marketing a referral system for students and families.2,6–9 To establish a referral system, school health personnel should identify health-care services and school- or community-based programs that encourage healthy eating and physical activity and address obesity and eating disorders. These services include

  • School-linked health clinics
  • Local health departments
  • Universities
  • Medical schools
  • Outside health-care providers (e.g., private physicians and dentists, hospitals, psychologists and other mental health workers, pediatric weight management clinics, community health clinics, managed care organizations)
  • Community-based nutrition and physical activity providers and services (e.g., dieticians, recreational programs, cooking classes)

The list of referral services should be based on the health needs of the student population, barriers to health care in the community, past student use of community services, and current community culture. Health, mental health, and social services staff members can assess which services are available at the school and which require outside referral.9 The list should include services that are accessible to all students, including those with low family incomes or without health insurance or transportation. If feasible, arrangements can be made to bring community-based services to the school. With a comprehensive referral system in place, health, mental health, and social services staff members are able to respond to requests from families seeking guidance and increase access to care among students.1

References

  1. Howard KR. Childhood overweight: parental perceptions and readiness for change. J Sch Nurs. 2007;23(2):73–79.
  2. Taras H, Duncan P, Luckenbill D, Robinson J, Wheeler L, Wooley S. Health, mental health, and safety guidelines for schools; 2004. Available at http://www.nationalguidelines.orgExternal.
  3. Barlow SE, Dietz WH. Obesity evaluation and treatment: expert committee recommendations. J Pediatr 1998;102:E29. Epub Sept. 1, 1998. Available at http://pediatrics.aappublications.org/content/102/3/e29.full.htmlExternal.
  4. Himes JH, Dietz WH. Guidelines for overweight in adolescent preventive services: recommendations from an expert committee. The Expert Committee on Clinical Guidelines for Overweight in Adolescent Preventive Services. Am J Clin Nutr 1994;59:307–16.
  5. Whitlock E, Williams S, Gold R, Smith P, Shipman S. Screening and interventions for childhood overweight: a summary of evidence for the U.S. Preventive Services Task Force. Pediatrics 2005;116:E125–44. Epub July 1, 2005. Available at http://pediatrics.aappublications.org/content/116/1/e125.shortExternal.
  6. American Academy of Pediatrics Council on Sports Medicine and Fitness and Council on School Health. Active healthy living: prevention of childhood obesity through increased physical activity. Pediatrics 2006;117:1834–42.
  7. National Association of School Nurses. Position statement: overweight children and adolescents. Silver Spring, MD: National Association of School Nurses, Inc; 2002. Available at http://www.nasn.org/PolicyAdvocacy/PositionPapersandReports/NASNPosition Statements FullView/tabid/462/smid/824/ArticleID/39/Default.aspxExternal.
  8. Rose BL, Mansour M, Kohake K. Building a partnership to evaluate school-linked health services: the Cincinnati School Health Demonstration Project. J Sch Health 2005;75:363–9.
  9. Allensworth D, Lawson E, Nicholson L, Wyche J, eds; Institute of Medicine. Schools and health: our nation’s investment. Washington, DC: The National Academies Press; 1997.
Safeguard 10. Provide all parents with a clear and respectful explanation of the BMI results and a list of appropriate follow-up actions.

Student BMI results should be sent to parents by secure means, such as by mail, and not brought home by students. To reduce the risk of stigmatizing students, letters should be sent to all parents.1–2 To avoid giving the impression that a diagnosis has been made, the letters to parents about students who need further evaluation—those classified as underweight, overweight, or obese—should avoid definitive statements about the student’s weight category.3 For example, letters might

  1. State that the student’s BMI result “suggests” that he or  she “might be” overweight.4
  2. Identify the student’s height, weight, and BMI-for-age percentile, and include a table defining BMI-for-age percentile categories with images.5
  3. Communicate that the student’s weight was found to be low/normal/high for his/her height and age.6

All letters should strongly encourage parents to consult a medical care provider to determine if the student’s weight presents a health risk.7

Letters to all parents, including those whose children have been classified as normal weight, should include scientifically sound and practical tips designed to promote health-enhancing physical activity and dietary behaviors. For example, the letters might encourage families to consume a healthy diet based on the US Dietary Guidelines for Americans.8 Parents should also be aware that young people should engage in 60 minutes or more of physical activity each day9 and reduce sedentary screen time such as television, video games, and computer usage. The letters should be written in appropriate languages and at appropriate reading levels to be understood by parents; the tone should be neutral to avoid making parents feel that they are being blamed for their child’s weight status.10 Motivational messages included in the letters should be guided by sound communication and health behavior change theories. To ensure comprehension and effectiveness, the letters can be tested with representative parents in advance.

If all 10 of the safeguards described above are implemented, BMI results may also be shared directly with older students–the Michigan Department of Education recommends that results not be shared with students below grade 4–as long as staff ensure that this communication remains private and does not stigmatize or label the students.11 Because these letters could have a significant impact on the students, the school nurses and school counselors should be prepared to deal with such reactions as anxiety and despair.

The letters should include

  1. Contact information for the school nurse or other school-linked medical care provider.
  2. Educational resources for weight, nutrition, and physical activity.
  3. Contact information for community-based health programs or medical care providers who treat weight-related health problems (including programs for those without health insurance).
  4. Information on school- and community-based programs that promote nutrition and physical activity.

Existing screening programs have developed standardized letters tailored to the weight status of the child.4–6 Examples are listed below.

References

  1. Byrd S. Dealing with controversy: the lessons of implementing BMI screenings. NASN Newsletter. 2003;18(1):18–19.
  2. Johnson A, Ziolkowski GA. School–based body mass index screening program. Nutr Today. 2006;41(6):274–279.
  3. Scheier LM. School health report cards attempt to address the obesity epidemic. J Am Diet Assoc. 2004;104(3):341–344.
  4. Arkansas Center for Health Improvement. Health Letter to Parents. Little Rock: Arkansas Center for Health Improvement; 2006. Available at: http://www.achi.net/BMIContent/Documents/120708_CHR_English-final_for_web.pdfCdc-pdfExternal.
  5. PennState Hershey, ProWellness Center. BMI Screening Letter. PennState Hershey; 2014. Available at: http://prowellness.vmhost.psu.edu/prevention/understanding_risk/bmi/bmi-screening-letterExternal.
  6. Ikeda JP, Crawford PB. Guidelines for collecting heights and weights on children and adolescents in the school setting. University of California Berkeley, Center for Weight and Health; 2005. Available at: http://cwh.berkeley.edu/sites/greeneventsguide.org.cwh/files/primary_pdfs/bw_weighing_0.pdfCdc-pdfExternal.
  7. Whitlock EP, Williams SB, Gold R, Smith PR, Shipman SA. Screening and interventions for overweight in children and adolescents: a summary of evidence for the U.S. preventive Services Task Force. Pediatrics. 2005;116(1):e125–144.
  8. US Department of Agriculture, US Department of Health and Human Services. Dietary Guidelines for Americans, 2010. 7th ed. Washington, DC: US Government Printing Office; 2010.
  9. US Department of Health and Human Services. Physical activity guidelines for Americans, 2008. Washington, DC: US Department of Health and Human Services; 2008.
  10. Dietz WH, Robinson TN. Overweight children and adolescents. N Engl J Med. 2005;352(20):2100–2109.
  11. Haller EC, Petersmarck K, Warber JP, editors. The role of Michigan schools in promoting healthy weight. Lansing, MI: Michigan Department of Education; 2001. Available at: http://www.michigan.gov/documents/healthyweight_13649_7.pdfCdc-pdfExternal.
Key Resources

Body Mass Index Measurement in Schools (Article)External [PDF – 239KB]

This article describes the purpose of school-based BMI measurement programs, summarizes the research, and recommends safeguards for schools choosing to engage in this practice.

BMI Measurement in Schools Executive SummaryCdc-pdf [PDF – 2 MB]BMI Executive Summary Cover

This executive summary covers key points from the research article. 

  1. Byrd S. Dealing with controversy: the lessons of implementing BMI screenings. NASN Newsletter. 2003;18(1):18–19.
  2. Johnson A, Ziolkowski GA. School-based body mass index screening program. Nutr Today. 2006;41(6):274–279.
  3. Scheier LM. School health report cards attempt to address the obesity epidemic. J Am Diet Assoc. 2004;104(3):341–344.
  4. Arkansas Center for Health Improvement. Health Letter to Parents. Little Rock: Arkansas Center for Health Improvement; 2006. Available at: http://www.achi.net/BMIContent/Documents/120708_CHR_English-final_for_web.pdfCdc-pdfExternal.
  5. PennState Hershey, ProWellness Center. BMI Screening Letter. PennState Hershey; 2014. Available at: http://prowellness.vmhost.psu.edu/prevention/understanding_risk/bmi/bmi-screening-letterExternal.
  6. Ikeda JP, Crawford PB. Guidelines for collecting heights and weights on children and adolescents in the school setting. University of California Berkeley, Center for Weight and Health; 2005. Available at: http://cwh.berkeley.edu/sites/greeneventsguide.org.cwh/files/primary_pdfs/bw_weighing_0.pdfCdc-pdfExternal.
  7. Whitlock EP, Williams SB, Gold R, Smith PR, Shipman SA. Screening and interventions for overweight in children and adolescents: a summary of evidence for the U.S. preventive Services Task Force. Pediatrics. 2005;116(1):e125–144.
  8. US Department of Agriculture, US Department of Health and Human Services. Dietary Guidelines for Americans, 2010. 7th ed. Washington, DC: US Government Printing Office; 2010.
  9. US Department of Health and Human Services. Physical activity guidelines for Americans, 2008. Washington, DC: US Department of Health and Human Services; 2008.
  10. Dietz WH, Robinson TN. Overweight children and adolescents. N Engl J Med. 2005;352(20):2100–2109.
  11. Haller EC, Petersmarck K, Warber JP, editors. The role of Michigan schools in promoting healthy weight. Lansing, MI: Michigan Department of Education; 2001. Available at: http://www.michigan.gov/documents/healthyweight_13649_7.pdfCdc-pdfExternal.