Percentiles are the most widely used clinical indicators for assessing the size and growth patterns of children in the US and other parts of the world. Percentiles give an estimate of a child’s position by comparing him with a group of other children, and showing what percent of this reference population the child will match or exceed. To help you understand it better, a 5-year old boy whose height is at the 25th percentile, is as tall or taller than 25 percent of the reference population for 5 years old boys. It also shows that he is shorter than 75 percent of the 5 year old boys that were used as the reference population.