Kids will only do behaviors that they are allowed to do. So, I believe every kid screams at some point, my sisters' did for months when they were young. Mine did two, but each of my kids only did it a couple of times. When they would first scream, I would bend over to get eye level and sternly say "No Screaming!" If they did it again, I lightly patted their mouth. Hard enough to create an element of surprise, soft enough to not be "hitting them in the face", then I would at the same time say "Mommy said NO screaming". I did this each time they screamed, which was only a few times, and they learned it wasn't acceptable and they stopped. Now, to show the other side of this one....my sister was never one to discipline the kids very much. She mainly waited until they were way out of control, and then would get mad and say "STOP IT!!!" Because of this, the screaming was absolutely difficult to be around. We would be going through the mall and her kids would be SCREAMING! Just for FUN!! It was ridiculous!! People were looking, I was having trouble concentrating well enough to carry on conversations, it was awful. So at one point, very early on, I said, "Ang, aren't you going to stop him?" She said "It's no use, he'll just keep on doing it" So, I said "not if I can help it" and I stopped the stroller, went around to the front of it and knelt down. I said "Aaron, NO SCREAMING" and the first time he did it after that, I leaned over the stroller and bopped him on the mouth and said "Aaron, NO" Soon, he stopped doing it, although he gave his mother a very pouty and offended look since he wasn't used to not getting his way. You just have to set boundaries and stick to them. Otherwise, the kids end up running the house.