If I took my 4 month old Black Russian Terrier puppy to a class and the instructor said to use a prong collar I would not return back to that class. Just my opinion, but I would never use a prong collar on a puppy no matter how big it is.

Dear Bonnie: I used to have the same problem when I took out my three dogs for a walk. Here is what I did. First of all I trained the wait command. I started out with the dogs very close to me, gave them the sit command (something they know) and then asked them to wait , (with my hand in front of their faces, like the stay command.) I reinforced this command at feeding time, when I went out the door to the yard, or in the door in the yard, or attached their leash to their collar. I worked on this before I took them out in the car, or out the front door. Then as they began to understand, I started to ask them to wait at the sliding door. (this is the door we exit to go in the car, or for a walk) After they were good at that, then the real test began. With a leash attached I would open the sliding door and say wait, of course in the beginning they would want to dart out.
As they waited I rewarded them and made a huge deal that they didn't go out the door. After that was occomplished and they knew what was asked, if they tried to bolt out, I would correc them, either by shutting the door in their face, or a slight pop on the leash. Then when that was occomplished we learned to step out of the slider after I went outside first. Then I would call them to me. Of course treating all the way. As their self control got better, I asked them to sit once they came out of the door. Then we took them to the car. Any pulling, I just stopped. I asked them to sit at the door, and then began to teach them the in command.They can't go in the car until I say
"in". This took a while, they were so excited they thought they were home free. Now I can walk them calmly to the car, but I am always on the alert to stop any disobedience and go back to square, one, two or three. I used a flat collar in this training. Now your baby is only 4 months old, so remember your pup is just a baby. Mine were a year old when I taught them. I think this could be taught to a younger dog, but I adopted mine at one year old.
Another step I have added, is placing a mat in the car and as each one gets to go "in" I ask them to go to their mat. They love it! Thanks Ed for all the training videos, I am so glad I taught my gang to go to their mats.
Hope this helps