I don't agree with everything in Dahlia Lithwick's Constitution Day column, but I agree about this:
You say you've never heard of Constitution Day™, a federally mandated holiday. Well, that is probably because it's only been a federally mandated holiday since 2004, when Sen. Robert C. Byrd of West Virginia invented it in much the same fashion that all of our greatest national festivals have come about: He tucked it into a massive appropriations bill. The relevant rider of the Omnibus Spending Bill of 2004 amended Title 36 of the United States Code (Patriotic and National Observances, Ceremonies, and Organizations) by substituting "Constitution Day" for "Citizenship Day."
Constitution Day commemorates the signing of the U.S. Constitution on Sept. 17, 1787, and also celebrates "all who, by coming of age or naturalization, have become citizens." The law itself provides that all educational institutions receiving federal funds—which means virtually all of them—must offer up some sort of educational program about the Constitution. It also requires that the head of every federal agency offer each employee educational and training materials about the Constitution on that day. If Constitution Day falls on a weekend, as it did in 2005, 2006, and 2011, it is observed on the contiguous weekday.
Now, mandating the nationwide teaching of the document that protects the most fundamental American freedoms may itself be unconstitutional, as Nelson Lund and the Heritage Foundation noted back in 2006. But, of course, that is just one of those idiosyncratic things that makes the holiday so special.
If you follow the Heritage and Lund links, you'll see strict-constructionist arguments of a sort that Slate writers do not usually endorse. I'm not complaining; it's just odd that this, of all possible issues, is where the site would find room for those ideas. I suspect Lithwick just couldn't resist the #SlatePitch contrarianism of suggesting Constitution Day is unconstitutional.
Whether or not she's right about the legal question, I don't think federal education mandates are a good idea. In this case, the mandate has the additional problem of being confusingly vague, since "all educational institutions receiving federal funds" is an awfully broad category. And that leads us to my favorite detail in Lithwick's article: "In 2005, when the law first went into effect, massage schools and cosmetology programs evidently flew into a collective panic over how to meet its requirements."
Bonus link: From the Yes, Libertarians Like To Argue About Things You Thought Were Settled files, here is Reason's 1987 debate, "Did the Constitution Betray the Revolution?"