I was hit for being naughty, usually by my mother, during my pre-school days. After that, the hitting from them mysteriously stopped. Somehow they learned that hitting didn't really have any effect on me, positive or negative.
I recall one day that I won't ever forget, a day when my grandparents babysat us one summer. They were getting annoyed with my sister and I, for whatever reason that makes little children annoying. This was the only time my grandfather (who passed away a little over a month ago) had raised his voice at my sister and I. Of course this just made us egg him on. He hit us, and we claimed that it didn't really hurt at all. Then, he said this which will never leave my head:
"It doesn't hurt? I'LL MAKE IT HURT!"
He hit us again, considerably harder this time.
When mom learned of this when she got home, she scolded him, and told him that neither she nor our father believed in spanking us. They pretty much stopped babysitting us after that, and my mother opted for a girl who lived down the street whose younger brother was coincidentally friends with my older brother.
So does spanking really help? From my experience, not really. Then again, besides those mentioned times, I was usually well behaved.