4 mth old German Shepherd

Question
I have a registered German Shepherd that just turned 4 mths a couple days ago.  I got him at 8 weeks and he was cute and chubby.  He is a very smart dog.  He plays but listens well and isn't too hyper.  We are signed up to start obedience school in 2 weeks.  Anyway, he was worm free on his first fecal but then I saw worms in his stool and have since wormed him twice (we start the 3rd time tomorrow) every two weeks and then will have another fecal in two weeks.  He broke his left rear leg at 11 weeks and was in a cast for four weeks (having it changed weekly was NOT fun).  He is small for his age.  He is only 31 lbs.  The vet told me not too worry that much of his growth probably went to heal the leg (his leg is perfect with no noticable limp now).  His mom is 85 lbs an dad 90 lbs.  I love your board, it had given me a wealth of information but now am worried because it says they usually double their weight at 4mths for a total weight which would only put him at 62 lbs as an adult!

Answer
If your vet is correct that healing the leg slowed growth, then he may more than double the 4 month weight.  I wouldn't count on it.  My 14 month old Lab Holly wasn't the runt of the litter, but is only 50 pounds, much smaller than her siblings.  Some dogs just turn out smaller.  I think many dogs have more than 50% of their adult size by 4 months.  

I would switch him to adult chow if you are feeding a puppy chow.  That will delay reaching his final adult size, but give him more time to develop the sturdy joints he needs for a long, active life.