Body Composition (BMI)

For the 9–18+ age band, body composition is again assessed using the Body Mass Index. The purpose, equipment and procedure are exactly the same as for the 5–8 band, so the full height- and weight-measurement protocol described under BMI (section 6.1.1) applies here without any change.

As a reminder, BMI is found from body weight and height:

A higher BMI usually indicates a higher level of body fat. Height is recorded to the nearest 0.1 cm and weight to the nearest decimal fraction (for example, 25.1 kg).

Why the Same Test Is Reused Across Age Bands

BMI is kept identical across both bands deliberately, because the measurement protocol — how height and weight are taken — does not need to change with age, only the interpretation of the resulting number does. A BMI of 19 means something different for an 8-year-old, a 14-year-old and an 18-year-old, because the normal range of body composition changes through childhood growth and puberty.

Interpreting BMI for School-Age Students

Unlike adults, where fixed BMI cutoffs (underweight, normal, overweight, obese) are commonly used, school-age students are usually assessed against age- and gender-specific BMI percentile charts, because a healthy BMI value genuinely shifts as a child grows. A single BMI number without reference to the student's age and gender percentile can be misleading on its own.

Worked Example for This Age Band

A Class 10 student (age 15) weighs 55 kg and is 1.65 m tall.

• Step 1 — Square the height: 1.65 x 1.65 = 2.7225.
• Step 2 — Divide the weight by this value: 55 / 2.7225 = 20.2.

BMI = 20.2 kg/m², which would then be checked against the age- and gender-specific percentile chart for a 15-year-old, rather than judged on the raw number alone.

Common Mistakes & Precautions

• Comparing a student's BMI to adult cutoffs instead of an age-appropriate percentile chart.
• Weighing a student in shoes or with a heavy school bag still on, which inflates the recorded weight. …