I had a year of American government around 9th grade-ish, which covered the basics of the system, the founding documents, etc. and then spent a lot of time with the formative debates driving it (Federalist/Anti-Federalist Papers, Montesquieu, Hobbes, Locke, and such). Plus during elementary school a year or two of American/state history, which had civics elements. Then there were sundry courses like geography and things like read-alouds covering topics like economics (I definitely recall learning about inflation and the labor movement in middle school).
American Government was also a required course at uni (which I believe is common among liberal arts schools). That one was more practical in focus.
Back in first grade I remember participating in a mock election based on the candidates of the day...
Bear in mind I was homeschooled for much of the above, and many of the homeschoolers I knew were already very civically engaged with volunteering, Boy Scouts, interning at the state capitol, and more.
Maybe that was just my social group, but we as a family weren't political activists or anything (nor was politics a particularly common or passionate discussion) and some of this was just the path laid out by the curriculum.