I think there are two things one wants to do when raising a kid. One wants to have the kid understand what they're supposed to do, and one wants the kid to actually do what they're supposed to do.
With a sufficiently bright kid, explaining what you want them to do and why is going to have them understanding it. You may have to take it to several levels on the "why", and that may lead to you challenging your own parenting assumptions, but if you really want a kid to do something, they've got to want to do it themselves, and understanding that it's something that will benefit them is going to help with them wanting to.
The other half, of course, is getting the kid actually doing it. Understanding it alone will provide impetus for maybe up to five instances of the kid actually doing it, if you're lucky. If you're not lucky, the kid will understand the theoretical portion of it, and still won't want to do it, because there's no immediate benefit for doing it. So you have to make it a habit, or provide motivation in some way.
And that's where the behaviorist stuff comes in. You tell the kid that the ultimate goal is whatever the ultimate goal is, and part of the way to get there is to get this task (whatever it is) done. And part of that is making something or other so it happens every time. I believe in getting consent from the kid for the conditioned change in their behavior.
For quite a while, Little Fayoumis was having trouble responding to hails when he was focusing on something else. Most kids who can attain that level of focus do. I explained to him that we wanted him to respond when we called his name. He already understood the theory. The theory was doing him absolutely jack when he was focused elsewhere. So, we went briefly over the theory once again (reinforcement is often good) and then we practiced.
"When I say your name, you say, 'What?', okay?"
*massive giggling from Little Fayoumis*
*glee from LF*
We repeated this for what was probably about five minutes, and we continued testing it throughout the day. He got to accept the "Yay!" as a valid reward. (Giving a kid a large reward on a regular basis, though it may be satisfying for both, isn't a good precedent to set, as they'll expect large rewards as their right thereafter, and unless you're prepared to continue this for a long time if not forever, avoid it.) He now expects cheering (clap hands, "Good job", "Yay!" and the like) when he does well on something, which is a reasonable reward, and can be given as many times as necessary without a problem. (Unless, of course, sore throat or sore hands or something.)
Regular re-evaluation by the kid as to why they're doing something is a good thing. This helps eliminate the rat-on-treadmill problem. "Do you know why you're washing your hands?" "Because it's good?" "What makes it good?" "It does good things?" "What is the good thing that it does?" "...it's good?" "It gets the germs off your hands. Germs make you sick. So, you wash your hands so you won't get sick." "Oh."
I think it's unethical to condition someone who is capable of giving consent without their consent. I think that conditioning a kid to do something without having them consent first isn't going to get the results either of you wants, and is going to open them to manipulation later. If they're used to having their conditioning regularly explained and agreeing that yes, it's a good thing, they are more likely to reject uninformed, unconsented conditioning later.