I dunno. I was in advanced classes starting in the sixth grade; everyone in the classes had a pretty good grasp of such things, and I'd hazard to say that most school children have a better grasp of the Bill of Rights than most adults.

Even in the "average" classes I was in, we'd cover a whole range of topics and ideas, and most of the people would "get" them. Of course, we were also dissecting and analyzing news articles in elementary school as part of the social studies component.