On Saturday mornings from 1973 to 1985, ABC filled the gaps between children's shows with three-minute animated lessons, using catchy music to explain the basic principles of grammar, arithmetic, history, science, government, computers, and money management. The public-service announcements were known collectively as Schoolhouse Rock, and the fact that few adults under 35 needed the preceding introduction is a tribute to the series' enduring power. Generations have bonded over their shared memory of Schoolhouse Rock's "Conjunction Junction"; some boast of having passed high-school civics thanks to the near-weekly repetition of "I'm Just A Bill" and "The Preamble." Schoolhouse Rock remains in the running with The Brady Bunch or Happy Days as the premier bit of "Hey, remember...?" '70s TV ephemera. The dewy-eyed respect for the series would be kind of pathetic if the songs and cartoons themselves weren't so charming and informative. The handy DVD Schoolhouse Rock: Special 30th Anniversary Edition contains all 46 installments on a single disc, and adds an additional disc with background info on their creation and a look at their continuing impact on American culture. Following the subtle changes in art direction (from Peter Max billboard psychedelia to cutesy minimalism) and music (from melodic country-folk-pop to complex, practically chorus-free neo-Broadway) makes for a telling study of trends in popular art and advertising. Repetition remains key throughout the run, but later lessons stick more with jokes and colorful characters, shedding some poignancy and emotional appeal. Oddly, the quintessential Schoolhouse Rock cartoon came late, during a brief mid-'90s revival. "The Tale Of Mr. Morton" features a hummable song written by series mainstay Lynn Ahrens and sung by beloved "Bill" voice Jack Sheldon; it's a touching story about a lonely man working up the courage to ask a woman to marry him, and it's almost beside the point that the cartoon doubles as a clear explanation of how subjects and predicates work. The best Schoolhouse Rock installmentsand there are many, "Scooter Computer & Mr. Chips" asidediverge from the topic at hand for lyrical moments: the way "Figure 8" concludes with a slide into infinity, the way "3 Is A Magic Number" includes the sweet lines "A man and a woman had a little baby / There were three in the family," and the way "The Good 11" giddily explicates how easy it is to multiply by 11. The Schoolhouse Rock worldview integrates educational principles into the everyday world, as if they were neighbors, or trees visible from a bedroom window. That's a lesson itself: how to become an integral part of American pop culture.