This is our second GSD. Our first GSD was laid back, very calm and could be taken anywhere. Our second GSD was brought home when he was 10 weeks old. He turns 1 year old this week. We have two teenagers and kids ranging from 2 years old to teenagers coming to our house daily. Our GSD will bark and raise his hair at one of the boys that comes over daily. The younger sibling comes over and our GSD does nothing. Our GSD dislikes the neighbors behind us. In fact he jumped over the fence and tackled the one boy and mouthed him. This took place about 3 months ago. The kids continue to play in the back yard but they run away screaming when they see our dog. We turned on the electronic fence and added some decorative border so our dog no longer goes over. We also enrolled him obedience class which he just passed. I took our dog for a walk and the neighbors kids wanted to see him. I made him sit and the one boy was able to pet him. Our GSD immediately lunged and barked at the boy who he tackled a few months back. Why does our GSD pick certain kids to dislike? I would take our GSD to my daughters LaCrosse practice every day and had a little 5 year old girl walk him around the track. I also had boys play ball with him and he never shows aggression. Our GSD will also play nicely with some dogs and other dogs he has no tolerance for. He continues with his next obedience class next week. Although I am teaching him obedience I do not understand the breed enough to figure out why he acts like this. I really do not want him to be that "do not pet" type of dog.