How do growth chart percentiles work?

Identify PATTERNS. Growth charts allow us to determine whether the trend or pattern of a child's growth is healthy. This is crucial, because individual measurements may be +/-, due to squirming babies or slightly different measuring techniques. While it's tempting to focus on individual measurements, this often creates undo anxiety. The big picture--over time--is usually what matters most.
Look at growth. Growth charts show doctors how your child is growing compared to others of the same age and gender. These percentiles also allow doctors to see the pattern of your child's growth and watch it over time. We expect children to more or less stay along the same percentile as they grow older. A child in the 10th percentile means 90% of kids are bigger and 10% are smaller than that child.