BMIs in Your Child’s School: Why and what purpose do they serve?

girl on scale You may have heard or read that your child’s school is assessing his or her health, collecting BMIs, or providing nutrition and physical activity education.  What does all this mean to you as a parent or guardian, as well as to your child?  This article seeks to discuss BMIs, what they are, what they are used for, and if the benefits of collecting them outweigh the concerns that arise.

What is BMI?

BMI, or Body Mass Index, uses a child’s weight and height, plugs it into a formula and compares it to a range or norm.   The Center for Disease Control states that a BMI calculated result is a reliable body fat indicator for most teens and children.  Although BMI does not measure body fat directly, it can be used as an indirect measure.   An example of a direct measure of body fat would be underwater weighing or the Bod Pod (air displacement plethysmography).  BMI has the advantage of being less expensive than the direct measure methods and is much easier to perform.  The reasons for collecting BMIs vary per state and district.  Gathering information and improving educational endeavors are both important reasons for collecting BMIs in schools.   BMI is useful as a screening tool to help identify weight concerns and implement prevention education and interventions as early as possible.

How schools collect and use BMI

When the BMI is calculated, the number is plotted on the boy’s or girl’s BMI-for-age growth chart.  A percentile ranking is derived from plotting the BMI number and this percentile is used to assess growth patterns of the individual child.   Comparison is done with children of the same sex and age.  Four different categories of weight status are used to categorize the child or teen: underweight, healthy weight, overweight, and obese. The American Academy of Pediatrics and the Center for Disease Control recommend the use of BMI to screen children beginning as young as age 2. 

BMI is not suggested to be used as a diagnostic tool, but as a starting point for further assessment.  BMIs are meant to provide information and initiate conversations regarding ways to make healthy nutrition and physical activity choices.  As research has shown, overweight and obesity rates among children and adolescents have grown tremendously. The younger children are when they become obese, the more at risk they are for developing chronic conditions and problems later on in life. Some of these include: diabetes, high blood pressure, breathing problems, joint issues, as well as social and psychological problems like depression (1). Studies have also shown that there has been a generational shift in acceptance of obesity in children, making it more of a ‘norm’ than an identifiable health problem (2). This has made it harder for parents to accurately assess their children’s weight status (2). A recent study by the Journal of Pediatrics found that 83% of the overweight boys and 78% of the overweight girls were thought to be about the right weight by their parents (2).

Challenges and controversy

There has been controversy over whether the benefits of BMI surveillance outweigh the concerns of much of the public. One study looked at the impact of these programs on the effectiveness in reducing obesity rates among school children (4). Some common concerns that this study found included whether this increased attention to obesity would stimulate increasing negative body issues among children and cause them to engage in unhealthy weight loss strategies (4). Others included the initiation of unhealthy weight loss or diet changes by the parents without consulting their health care provider first (4). What is also common is the concern that these programs may be ineffective overall and deter from more successful focus based around improvements of the school physical activity and nutrition areas (4). Expert organizations still recommend using BMI surveillance as an effective screening tool (4). Although there needs to be more studies evaluating the effectiveness of these programs, with the proper use of guidelines and resources, BMI screening could become a more common, accepted, and useful tool in assessing and triggering interventions for obesity among children.

How to use BMI data

Each state and school district varies in the requirements or suggestions that the district receives.   According to a comprehensive study in Preventing Chronic Disease, 20 states were requiring BMI or body composition screening with 9 additional states recommending the screening as of 2010.  So how can you use the information coming home about BMIs? Firstly, find out whether your children’s school is conducting BMI calculations so that you may have access to the results. It is important to realize that not all school districts that are doing BMI measurements are sending the results home.  Some states and districts do send home results with information on how to interpret and use the information, while others are using them for evaluation of programming and interventions. 

Schools may you an send opt-out letter so that you have a choice in participating in the screening (3). Schools may also send out letters of notification if their child is categorized in the overweight or obese range based on their BMI plotted on the growth chart (3).

With it being more difficult for parents to identify overweight and obesity in their children, having the BMI results available can be a good starting tool to assessing their child’s health.

Naturally, there are many barriers in addressing potential weight issues with their children. As parents, you must have support to overcome these barriers so that you can have the confidence to take charge of their children’s health. A few tips provided by the Shape Up America! organization can help you discuss and start interventions with your children:

  1. “Communicate that your child is loved and accepted as they are today.” (3)
  2. “Make family changes in lifestyle rather than impose individual changes on the child.” (3)
  3. “Consult with your family health care provider before initiating dietary changes.” (3)

In summary, the BMI can be most useful when it is considered one additional tool in the toolbox.  It is not the only or end all tool, but one that can be a starting point for healthy conversations and another way that those implementing programming on health can determine if  their programming is having a positive impact and behavior changes are occurring.

The more knowledge we have about our health, the more choice we are afforded toward nurturing healthy behaviors.  Many factors must be taken into consideration with BMI and therefore it is crucial to remember that BMI calculations are not perfect or the one and only assessment that should be performed.  Age and gender are important to consider in this assessment.  The healthy level of the child or teen varies for age month by month and as his or her height increases. The intent of these requirements or suggestions is to increase awareness of weight-related risks in hopes of encouraging healthy lifestyle changes.


Liz Smith, Ohio State University Extension


Linchey, J. & Madsen, K.  (2011).  State Requirements for School-Based Screenings for Body Mass Index or Body Composition, Preventing Chronic Disease, 8(5).




(4) NihiserAJ, Lee SM, Wechsler H, McKenna M, Odom E, Reinold C, Thompson D, Grummer-Strawn L. BMI Measurement in Schools. Journal of the American Academy of Pediatrics. 2009. 124;589:597.