It's not a question of determining right or wrong, because most kids at that age are able to do so, it's a question of impulse control. Kids around that age (taking into account differing levels of maturity) will often do petty things wrong that get them into trouble. When asked if they knew it was wrong, they say yes. When asked if they knew they'd be caught, they say yes. When asked, "then why did you do it?" they can't give an answer. Their brains are still connecting those pieces. Do you know anything about child development whatsoever?
And since you decided to malign my mental acuity, I scored in the 90th percentile or higher of every standardized test I ever took, graduated high school at 15, graduated college at 19 and started working corporate at a Fortune 500 company the same year. The discussion in question isn't about intellect or a knowledge of right or wrong, it's about the ability for children of a certain age to make decisions based on their predictive knowledge of the future.
Link to prove I'm not making shit up
You state that a child of 12 lacks the mental capacity to evaluate the consequences of their actions. I said that is bull from both knowing my childhood, and that of helping raise kids.
Kids are typically well aware of their actions even at a young age. They may be impulsive and act when they should think a little longer, but that is something not exclusive to children. Heck, read these forums a bit more and you'll see my argument there.
But let us evaluate your example shall we? A child does an action they know is wrong. When asked if they knew it was wrong, most children will know it is wrong unless it was an action in an experience they have never had or can not relate to a previous experience. That is the mental capacity we all start developing at a very early age. My nephew of two knows not to run his toy Thomas the train on the back of the couch. He does it anyhow, but I'll explain a bit more why about that in a second. He does an action he knows full well is against the rules and is wrong. When asked if he knows that is wrong he states he does. When asked if he knows the consequences of taking that action, he states he knows it. When asked why he did it, he may do what many children do, shrug his shoulders and "cop out." Actually, most kids do the cop out part from question one if they think that will get what they want, which is attention, without the consequences.
Just because my nephew is too young to have the mental capacity to EXPRESS his motivations, does not mean he lacks them. This is where I have cause with your argument. Once taught that expressions and he proper results and consequences, people of all ages behave better.
So in my example, relating to yours, about my nephew and his actions you might be wondering why would my nephew put his toy on the back of the couch. This is easy, and comes in two parts. One, he wants attention at the time. He does this out of impulse to get attention, because he knows if he is caught, and he will be, I or another adult figure will catch him. He has rationalized what he believes the consequences of his actions to be worth the risk of drawing that attention. This is because he, even at two years old, he feels a scolding is worth the risk at this point for attention because a scolding is all he has received for such actions thus far. The second part is because children are always testing the boundaries of their environment, which includes rules imposed on their behavior. They know something is wrong, they know the consequences, they may even rationalize enough to accept the consequences prior to action (in which case it something not done on impulse which they also do), and still act. This is more instinct here than mental function. The instinct is to check that the boundary as they believe it to be still exists. It is a natural ANIMAL instinct and can be viewed in every species on the planet. To explore, to test, and constantly verify ones surroundings.
As a parent or an authority figure, one must recognize all aspects of why an action was committed. Children are rarely as naive as many people make them out to be. So going back to the example with my nephew, what would be my proper course of action(s) to deal with the situation? After realizing what his actions were about here is what I did to correct the behavior.
1) impose a harsher punishment and explain to him that the more he continues this action, the harsher the punishment will be. Explain in detail what further punishment may be. This causes my nephew to re-evaluate the risk versus reward scenario. Doing this on my part MAY be enough to correct the behavior, but it may not. So the next part is...
2) To explain the proper course of action I want him to take an alternatives so he can get what he wants, in this case attention, without any consequences. Now that my nephew understands he has a proper channel that has no risk and all reward while further actions I do not want him doing will impose higher risks/punishments the behavior gets corrected.
Sorry for the long winded diatribe, but the main point of my post is I KNOW through personal experience and psych studies that kids have a much greater mental capacity than adults give them credit for. Actually, I remember reading somewhere (wish I remember so I could provide the link) that kids actually have a much larger mental capacity than adults. The problem is they lack the experience(s) to which to use that capacity. Hence why they need proper teaching.
Again, I point out that kids are not impaired by their age that prevents them from making "predictive decisions of the future" at all. They are fully capable of doing so. Kids, just like adults, make decisions for the future based on experiences of the past. Just like adults, if they don't have enough experiences or have received improper ones, they will make bad decisions. That has nothing to do with age what so ever.