M.I.
ok, my question to you is, if your son is physically active, east well, gets plenty of sleep, and (you dont say, but im assuming) is otherwise happy and healthy, why on earth do you care what percentage he is?
you know what? those percentage charts are the most stupid rediculous things ive ever seen. their ONLY PURPOSE is to compare kids to one another. thats their ONLY PURPOSE!! the reason doctors use them is to watch a childs growth over time. generally, they like children to stay within the same numbers. a 90 to 75% drop to me is no big deal. your doctor would have said something if it was a big deal. if he had gone from 90% to 20% it might have been an issue for a minute; he might have asked if your son ate enough, or whatnot. i suppose in some cases, they would test a child for growth issues. but i see no problem with your son still being larger than 75% of kids his age.
this isnt a score of his intellegence, this isnt a score for his personality or kindness, this isnt a test. it simply means that he 75% of kids are the same size or smaller than your son. 75% of kids are smaller than him! so in the grand scheme of things, hes doing just fine, size wise. just keep doing what you are doing; you are doing a great job with your son. dont let these stupid irrelevant charts mess with you; its just a tool doctors use. its not fair, but for some reason they think these archaic things will help them find problems "before they start or get too far" or something. i mean, really, if you had a child who went from 90% to 20%, you would notice something FAR before they put him on a chart (and really, any doctor should notice it too!). its simply unfair for them to do this to parents, and not explain what they are using them for .
heres a link that will help you.
http://www.babycenter.com/0_growth-charts-understanding-t...
but like i said, dont stress over this. its not a big deal. your son is growing at HIS OWN RATE, not someone else's. and your doctor would say something if something was wrong. i think your instincts about him and puberty are spot on. YOU know your kid. YOU would know before anyone else if something was wrong with his growth. just keep up the good work! :)