Beating sounds like you're taking out your failures on your kids.
Spanking is when you realize that the reprecussions from them not getting a lesson through their head, like don't run in the street or don't touch something hot is far worse than a swat to the hand or bottom. And it's easiest to associate what not to do with minor pain. It's the easiest thing to comprehend. So my kid gets a slap to the back of the hand and doesn't get hit by a car. Fair trade off.