I was 5'-1" and weight 115 at the end of my 8th grade year. When I came back in the fall as a freshman, I was 5'-10" and weighed 175. What's more, I had always kept my hair cut in a butch cut in elementary and junior high. That summer I let it grow out and it was curly! Who'duh thunk? And my voice changed to a resonating baritone.
I had people coming up to me who had known me since first grade saying, "Hey, welcome to our school! I'm ______________."
"Yeah, I know. I'm Mike. Mike! Yes ... Really!!"
Took some convincing for them to believe me. I went from playing wingback and safety on the junior high team to being the starting fullback and middle linebacker on the high school team, and before the season was over, I had put on another 30 pounds and grown another 3". I couldn't walk and chew gum at the same time!
Man, I could block and tackle though!