OP - you could be describing my family, and I have to say, I think most of it is pure personality. Sure, I think we are good parents, but the fact is, we were lucky to end up with a child who has from Day 1 been pretty content to sit quietly, follow directions, and otherwise be a very good kid. While I think DC2 bis going to be a bit more trouble, he has never encountered a piece of food he didn't want to eat; if you saw us in a restaurant, I'm sure he'd be so busy gorging himself he'd appear very well behaved!

I think a clear understanding of consequences is key regardless of temperament. If I throw my bread on the floor, will I get more bread or will I not get another piece?

Yes behaviour is taught..but some kids are a heck of a lot easier to teach than others. As all parents of more than 1 child know, the same parenting does not work the same way on each child. Some kids are more content to sit at a restaurant..doesn't mean they have great parents. Personally I don't think kids that require electronics to make it through a family meal are actaully behaving..they are just very entertained.

Manners are taught.

Impulse control, executive functioning, and temperment can intervene, and perhaps over time can be taught to be controlled. But not until perhaps the mid-to later elementary years, or even later for some kids.

When I took my twins to their first dentist appointment at 3 years old, they were angels. They waited quietly and patiently for the appointment that was delayed. One actually thanked the hygenist profusely for cleaning her teeth so well. They shook hands with the dentist, sat still during the appointment, complimented his ability to count all their teeth, and politely said goodbye at the end of the appointment. As we were walking out the hygenists told me that in 5 years of working there she had never seen two more well behaved kids and that I should be proud. (I was beaming).

Then she offered them each one toy from the treasure chest of cheapo stickers and plastic things. One of my daughters asked "please may I have two?" and when she was told no, she lost her ever loving shit. We are talking screaming, flailing tantrum on the floor of the dentist office.

Behavior is taught, but this preschool time, it's when we are all still teaching it...it's still a work in progress.