Hey I'm 18 I didnt start puberty till mid grade 9 maybe? It only started because the doctors were concerned that I wouldn't ever go through with puberty till I gained weight, i was only 90lbs in grade 9, SO they gave me a feeding tube on came the weight and the puberty!
So if your skinny and small and you dont have a feeding tube look into it ask your doctor, also I would suggest ensure plus with meals at school, and scandi shakes with meals at home, just for extra calories, also deep fried food at home when you can!! hope this helps!!