When I was a senior in high school our history class was called American civics. The class taught us about how our gov was supposed to work. It also taught us about politics and the two party system. Gerrymandering was a way both parties strengthend their hold on power. You could carve out districts and precincts that favored your party whenever you had majority control. You have to take a college level political science class to learn this basic stuff now.
Maybe a few people have a bit of an idea of what it might be but not understand it completely. I didn't even know until I had to look it up for my English class a few months ago. But it is true that most Americans do not know much about it. But it also depends on many reasons to why they might not know.