Weighing In... Should Schools Assess Body Mass Index (BMI)?

Are schools crossing the line when they measure body fat through BMI scores?

Posted Apr 06, 2015

Flickr Creative Commons/Paul H
Source: Flickr Creative Commons/Paul H

Weigh in time... A second grade girl brings home a letter from her school revealing her Body Mass Index (BMI) scores taken in September 2014 and March 2015. Her scores didn't fall within the "healthy range". So puzzled by the letter, the little girl got off the bus and asked the troubling question, "Does this mean I’m fat?" Clearly not a question any parent would want to be asked by his/her child. 

Here are some questions for you... Did the school cross the line by not developing a confidential and educational procedure for notifying parents about the assessment? Should the school have conducted a BMI assessment in the first place? That's a question seems to have mixed answers. With childhood obesity at an all time high, many health experts believe school-wide BMI screenings are a great way to identify and intervene with children being overweight and obese.

Did you know that approximately 25% of schools in the US require BMI measurements? There are even electronic sources for schools to use to keep track of the large quantities of BMI data. For example, the Centers for Disease Control and Prevention (CDC) developed the Children's BMI Tool for Schools that computes BMI for up to 2000 children; so a lot of schools utilize this source. But there are several unanswered questions. Like how are these screenings being conducted? Many schools line students up in physical education class and weigh them. Definitely an efficient way to get the measurements, but does it take into account the child's feelings? Furthermore, is it effective? 

Flickr Creative Commons/Lauren Manning
Source: Flickr Creative Commons/Lauren Manning

To begin to answer these questions it's best to understand BMI and how it's calculated. To address this issue, I turned to health expert Jonathan Armada, ACSM-HFS (a Crossfit trainer and competitor). Jonathon has been in the fitness and wellness industry for over 13 years and holds a BS in Exercise Physiology and an MA in Biomechanics.

Jonathon, explain BMI? Is it a good measure? Are there drawbacks to relying solely on BMI scores?

BMI is a ratio of your height to weight. More specifically, this ratio is calculated by taking your height in meters squared and dividing by your bodyweight in kilograms (m^2/kg). The number from this equation is used to categorize people as underweight, normal weight, overweight or obese). 

Below are the CDC's BMI calculators for Adults and Children:

Adult BMI Calculator 

Child and Teen BMI Calculator 

In general, this is a good tool to assess a large population quickly. This method does not take into consideration body composition or the amount of lean mass (muscle, bone, etc) and fat mass. BMI does not take into account if you have a lot of muscle, or large frame like a bodybuilder, or if you are a small person with a small frame with a lot of fat. So if you lift weights, are genetically lean and muscular, or play a sport that increases muscle mass, BMI can be misleading in terms of finding a healthy bodyweight. Lean, very muscular people, like sprinters, bodybuilders, and NFL wide receivers would have BMIs that put them in the overweight or obese category. Obviously, these people are not overly fat, but, again, BMI does not account for amount of muscle or fat.

A better way for you to find a healthy weight is to find a professional who can measure your body fat percentage. Finding a professional that is proficient at skinfolds and can analyze the results for you will be the best way to understand and maintain a healthy weight or help you get on a path to reach a healthy body weight. Two site skinfolds, tricep and calf, (Slaughter et al., 1988) have been used to find body fat percentages for children 8-18 years. Beyond 18 years of age, using a 7 site skinfold has been shown to provide better accuracy. There are handheld devices and weight scales that can estimate your body fat by BIA (Bioelectric Impedance Analysis), but these devices can have a lot of error in calculation.

Flickr Creative Commons/Ralph Aichinger
Source: Flickr Creative Commons/Ralph Aichinger

So, other than solely relying on BMI scores why aren't more reliable and comprehensive fitness assessments being conducted to determine whether a child's weight is in the healthy range? Should the schools be conducting these assessments or should it be left to healthcare providers? This appears to be a growing debate not only with the experts, but also with the public. Just this last November, a brave young lady took a stand against being weighed in front of her physical education class. Unfortunately, she was sent to the office for her refusal, but didn't she have the right to say 'no'?

Here is a link to the story in case you missed it.

For younger children shouldn't the parents and the child have the right to say 'no'?  But before it gets to that stage shouldn't the parent and child have the right to consent to the assessment? Weigh in with your thoughts... should schools be assessing BMI or are they crossing the line?


Slaughter MH, Lohman TG, Boileau RA, Horswill CA, Stillman RJ, Van Loan MD, Bemben DA. 1988. Skinfold equations for estimation of body fatness in children and youth. Hum Biol 60:709–723.