I'll go a different route. I'd say to not overdo it and preach patience. Baseball is a marathon and not a sprint. If your kid grew a ton in a year, he needs time to "grow into his body". Many kids I know who were very good HS pitchers had control issues immediately after they grew a lot. A year later, they seemed to be fine. Everything you work into your kid becomes "out of date" when he grows a bit more. Also, if he is growing a ton, overuse could become a bigger threat due to potential growth plate strains. As I said, I'd preach patience, which is easier said than done.