My oldest boy is 15 years old. Recently he has become violent and domineering. All the conversations that we have had with him haven't helped much. He continues to pretend that now he is 15 years old he has the right to be free and to behave as he pleases. When we threaten punishment, he doesn't want to hear about it. I want to spank him. Is it an effective punishment in this situation?
Even though your son is fifteen, he is still a child in your household. Unless he is able to live on his own, supporting himself with his own labor, he must live by the rules of your home, which should include being respectful to his parents.
What saddens me is that you have allowed the situation to develop to this point. Violence and disrespect don't just happen suddenly. Parents tolerate small instances of them, perhaps hoping they will go away. The child pushes further seeking what he can get away with until his parents are pushed to the breaking point and then they desire to lash back at their child in anger.
Spanking is an effective tool in dealing with violent and disrespectful behavior, but it will not work if you only employ it when you are pushed past your breaking point. While you are calm, sit down with your wife and lay out specific rules regarding what you two will and will not allow in your home. Think about what would be reasonable responses to when these rules are broken (and they will be broken). For example, hitting is no longer allowed. Any hitting will be punished with ten to twenty swats with the rod on the bottom. Any damage will be repair or replaced. Cursing, swearing, or backtalk to an adult in the home will be punished with five to fifteen swats with the rod on the bottom plus loss of any privilege being argued about for one week. This should get you started.
The list doesn't have to be complete. In fact, it is useful to start with a few things that are the worse examples of bad behavior and work at getting those under control before moving on to things that are not as bothersome. However, you and your wife need to sit down with your son and tell him that these will be the rules in no uncertain terms. In other words, stop making threats about punishment. It must become a non-emotional response. When a rule is broken, a punishment will be delivered. It also must be enforced consistently, even if it seems like you are doing nothing but delivering punishments for a while. You have years of bad habits to break. It will take time.
Punishment alone is insufficient to bring a change in behavior for an older boy. You also need to teach him the right ways to handle difficult situations. "The rod and rebuke give wisdom, but a child left to himself brings shame to his mother" (Proverbs 29:15). Explain to your son why the behavior is wrong and what would have been a better response. Talk about situations you see around you and discuss what went wrong and what were some of the alternatives. One of these days your son is going to be a citizen and a parent. Do you want your son, with his current knowledge running your town in the future?
As things begin to come under control, offer your son options in his punishment. Let him decide between a short but painful consequence versus a long drawn out one. This is what God did with David. "So Gad came to David and said to him, "Thus says the LORD: 'Choose for yourself, either three years of famine, or three months to be defeated by your foes with the sword of your enemies overtaking you, or else for three days the sword of the LORD - the plague in the land, with the angel of the LORD destroying throughout all the territory of Israel.' Now consider what answer I should take back to Him who sent me."" (I Chronicles 21:11-12). The crime is not left unpunished, but the choice becomes a learning process as well.