There is a difference between "beat" and "spank". I have two kids, a boy and a girl. With the girl I have always been able to talk things and she understands what is right and what is wrong. Just by telling her how disappointed I am with her behaviour, is enough for her to change it, as she need her parent's approval and it is a reward in itself. The kid, on the contrary, couldn't care less whether we are disappointed or not. He responds to signs of joy from his parents, but usually he does just what he pleases. For some reason, he doesn't have the same empathy than his sister, and therefore, the reward of his parents being happy with him is easily overshadowed by the instant reward he gets by disrupting his class, stealing somebody else's toys or just running into a tantrum just because you refuse to buy him the eleventh candy of the day. I use a "growing measures" approach.
First I try to explain why I do what I do. If it doesn't work, I try to remove the kid from the object of conflict and explain what is wrong with that -"i.e. the other kid wants to play with his toy, how would you feel if the tables were turned?", and if it doesn't work and the tantrum gets higher, I resort to spank him because once he is out of control, he is unable to calm down by himself and he will increase his level of agression, seeing than by merely crying and shouting doesn't give him results. He will start to hit, punch, and even ran away, completely out of control. I'm sorry, but having to face the decision of whether he will receive an spank or getting in danger for blindly running into the streets, I choose the former.
That being said, I would not let anybody spank him just because. It all depends on the kids age. Mine is just 4, but there are some unruly older kids that need some reality check about what is life like out of his home, overprotected shelter. Some years ago I was joking with some kids - I was like 35 and the kids were something like 11 or 12- I didn't know, it was just some joking on the streets about their bikes or the like. One of the guys spit me in the face. My reaction was purely instinctive - I spit him back. For one moment I felt like I had abused of my physical advantage, but the guy learned a lesson - you better think twice before spitting somebody older than you. Had his father seen me, I don't know what would have happened, but I would have not asked for apologies. If I knew somebody have spit my kid, but hat spit him back, I don't think I would have said anything - kids have to learn the lessons, and some lessons can only be learnt the hard way.
It snowed here a few weeks ago. My kids had never seen snow before. Regardless of how many times I told them, I couldn't keep them from eating the snow. It was new for them, and it didn't matter what I said, they had to test by themselves. Once eaten, they discovered it doesn't taste like ice cream, and it is nothing special indeed. Lesson learned, some lessons are better lernt at home, in controlled conditions, than out of home.
That's my .02 cents worth of parenting own experience.