I've got a group of characters in a long-spanning series I write, ranging in (final) height from 4'11" to 5'9", most of them being between 5'3" and 5'6" When I start the series, the first five are all about to start the fifth grade, and I'm thinking they reach final height (or close to it) at about 18 years of age.
Now, I've looked at growth charts for females but I'm still quite confused at trying to figure out the rate of growth. They keep roughly the same ratios to each other through the series--the shortest of them stays the shortest and the tallest stays the tallest, even though the average ones might switch who's taller by an inch for a while. (One of the somewhat running jokes is that the tallest of them has been drinking coffee since she was eight, and anytime someone mentions it stunts her growth, she says something along the lines of "At my current height, I'll take my chances.")
Roughly what height would the tallest, the average, and the smallest be in 5th grade, in 8th grade, and in 12th grade? I think I can work around those three points, especially if I can get some information on when growth spurts happen.
Thanks in advance if you can help me.