the first time i put a leash on zack, the same thing happened, he sat down and refused to come with me, he pulled against the leash. I foud myself dragging him. that wasn't how it was supposed to be. I ended up picking him up and putting him in the shopping cart (we were in a big pet store).
This was easily solved. I had a book at home called Puppy Preschool and it advised to take the puppy out on the leash but don't force her to go anywhere. Wait for her to walk, then go the same way she goes, you can even throw a toy for her to chase and just go with her while holding the lead. let her be the leader, make it fun, avoid any unpleasant struggles.
Do it for a short time, and do it again the next time, later in the day. Let her wear the leash around the house, as long as she's supervised and can't get tangled up or hung, let her get used to it, and let her learn that it's fun when you hold the leash and she is on the end of it. by the second or third day or sooner, she'll start walking the same way you are walking, you invite her to come with you while you hold the leash. There's no need to pull her, and it doesn't work to do that anyway. The book said in a day or so, he would be willingly walking on the leash, and that was what happened.
i use an Easy Walker harness, it clips in the front which greatly reduces the degree to which a dog can pull forward, compared to a clip on their back which they love to pull against. On the front, when they pull, it pulls them off balance a little, and that causes them to not pull or to pull less. I believe they have an extra small size, but you'd have to measure, and maybe call them and ask.
:dgwlk: