JRT puppy growling

Question
Hi, my husband and i just recently bought a Parson's JRT girl puppy who is 4 months old.  the first few days she was so great, excited, loving to everyone... and now she growls at almost everyone except my husband and i. she even nipped at our 3 year old nephew. she seems so timid around people when they come into the house.  she is so lovable and cuddly with my husband and i, its like a whole different dog around others. we have been correcting her when she starts to growl but it seems to have no effect on her. we also have been not letting her come sit on our laps on the couch when she is like that.  what are the appropriate steps? is this just a puppy thing??? I grew up with a short legged JRT who couldn't get enough of people. he was always so excited around strangers. so this behavior of our new puppy has really confused me.

Answer
The puppy has already shown signs that he thinks he is boss and you are his subordinates. He feels that anyone other than your husband and yourself are a threat and he is there to protect you and keep any potential harm away. In his eyes, you belong to him.  The Parsons are much more territorial and hunt instinctive, active and "uptight". There is a huge difference in the Parsons as opposed to the shorties. The shorties as you know are family dogs, the Parsons are better suited with one or two people who will give them 100% attention and sign them up for lots of activities like agility, racing or go-to-ground. They are amazing athletes, and with good, firm, proper training, can be great pets too.  I suggest taking her right away to either a Puppy Kindergarten Obedience class or Good Citizenship professional training school (NOT a PETCO) to get her trained and YOU back in control. LOTS of socialization with other people and dogs/animals is a must for this breed early on and this is why a dog training school would be good for her too. She's still young and you sound committed and knowledgeable so it should work out just fine, but don't waste any time, sign up right now. The dog trainer will show you exactly the right techniques to use to correct the aggression and turn it around to obedience. Once you learn the right way, you'll see great results. For me to go through each technique here would be hard because of the limited space, but these dogs need solid handling.  Definitely look into some fun classes too, like agility or go-to-ground as well as the obedience classes, you'll see she will excel and be the best dog in the class; and it will release lots of pent up energy the Parsons are so well known for. Don't worry, it's early and Jack Russells are super intelligent and learn very quickly, but don't wait! Best of luck with your new pup, you'll do fine.