American students are taught more about the Constitution than almost any other topic. Given the relative brevity of the document and this extreme emphasis(the Constitution is treated like the Bible/Torah/Koran in much of the country and the relative knowledge on that topic is a byproduct of this ), it's pretty easy to find people who know a lot about it and as a law student most everyone knows what most of the amendments, articles and important clauses cover by heart.
I agree there is some familiarity with PARTS of the Bill of Rights, but the TV show Law and Order has done more than the schools to promulgate that knowledge. I remember a survey of Harvard Seniors in which most of them identified "from each according to his abilities" as the US Constitution.
Several years back, I was doing several moths of insurance estimates for a law firm and worked directly with a rookie lawyer, and we chatted in the mornings. After the third time I showed him a file in my computers from Federalists and so forth on those points, he asked, 'how do you know the Constitution so much better than I do, and I just got an A in Con Law 18 months ago?' I told that's because you studied what judges SAID about the Constitution, like "substantive due process," which isn't in the Constitution.
And may I suggest that the Third Amendment appears unnecessary now, because the federal government is adhering to it, let's say, perfectly and no one is trying to change that.