I come from a long line of lecture-happy parents. This used to drive me nuts when I was a kid. I would get into trouble and then get an earful. My eyes would glaze over and I would basically just mentally vacate the premises. My own kids do it to me now. Here I am imparting my vast wisdom and experience on them, and all they can think about is "when can I play legos again". I've been reading a book called "How to talk so kids will listen, and listen so kids will talk". So far, I'm frustrated by the contrived examples given in the book. When I try to use the suggestions I get nowhere. How do you know when your kids have gotten your point sufficiently? I don't want to bore, or annoy them, but I do want to them to get some benefit from my talking.
It's best to save the longer explanations for a time when the child is calm and receptive.
So basically at the time they do something wrong, be very blunt and to the point. "Because you did A (a bad thing), you need to have a timeout", or whatever correction method you are using. At this point they're likely going to be very unhappy and stressed etc. and they aren't at all receptive to anything else you try to teach them.
Once the tantrum is all over and everyone's happy again, just broach the topic again gently. Something like...
"Do you remember when you did A, and daddy got cross, this was because doing A is very dangerous, and we don't want you to get hurt..." etc. etc.
Kids aren't that different to adults. Nobody learns effectively, or is receptive to new ideas when they're angry or upset. So, save the long explanations for when it may have a hope of sinking in.
Are you talking AT them or TO them? Mine do the eyes-glazed, mind-is-a-million-miles-away thing when I'm grumbling about this or that thing; when I see that look starting to threaten, I stop and ask them (a) what did I say, (b) why am I telling you this, (c) what will happen if you continue with [insert poor decision or behavior here]? If I'm not quick enough with the re-direct, I have to get the child's attention back on me, and start over, so it's training me to pay attention to THEM as well.
And when I actively discuss the situation with them ("why do we hold a hand in the parking lot/ not dart into traffic") and they respond with something that makes sense ("because the car is bigger than I am and you can't get another me from the kid store if I am hurt"), then I know they're listening. I can also see if the way I'm attacking the issue isn't effective, and either change my tactic or just drop the whole thing for a while.
This doesn't mean I don't end up having the same conversation over and over and over; this just means I'm hopeful that they are HEARING me and not just letting the words flow past their ears. I'll figure they have truly groked what I'm teaching them when the poor decisions or behavior I'm trying to address cease.
My kids are all grown now, but when they were little, my philosophy was that all discipline should be quick and decisive and then it's OVER and I do my best to establish that we are all still/again a loving family.
I haven't studied any psychological studies, but it seems to me that if you tell your child, "Hey, don't talk to your sister like that!" (or whatever the issue is, of course), the kid may get the message or he may not. But a 4-hour lecture on why it's wrong to be rude to your sister is not going to be effective because the kid will zone out, just as you describe. You make your point, and you stop. (Depending on the nature of the offense and the attending circumstance, a sharp scolding may be the all the discipline that's called for, or there may be something more, but that's a different question.)
When children are older, there may be times when it is appropriate to really explain the reasons behind something. If the child challenges something you have said, you should be prepared to back it up. I recall the time one of my children insisted that there was no need for her to finish school because she knew lots of people who worked at McDonalds who had nice cars and big houses, and I had to explain that this was pretty much impossible unless they had a bunch of money from an inheritance or some such.
But if your lecture is pretty much repeating the same point over and over -- it's wrong to hit your sister, you wouldn't like it if someone hit you, you should be nice to your sister, people should be nice to each other, etc etc -- I really doubt the child is learning anything by the repetition. I'd zone out too.
The authors of the book you are reading have an earlier book that is very interesting. It is the story of their discovery of Haim Ginott's ideas, and of their attempts (not always successful) to apply these ideas in their own family situations.
Here's a fun idea. Try a charades or pantomime approach. Whatever you need to convey to them, convey it to them through nonverbal means. When you're done with the disciplining, you can talk again.
Once in a blue moon, I suppose, this might not be enough. In that case, write down what still needs to be communicated. By hand. You'll run out of steam quicker that way than if you were yakking.
Or what about singing? My husband and I went through an interesting phase in which we had all our "vigorous discussions" entirely to the tune of "Streets of Laredo." We had to do this for a number of months at some point because Baby #2 got very unquiet and couldn't nurse, settle or sleep when we were carrying out any sort of vociferous discussion.
I kind of miss it.