For us in Chicagoland it ran on every Saturday morning on channel 7 (ABC). I don't know if it ran during the week or not. I loved them as a kid, and some of them actually taught me a few tricks to use in my school work, mostly the math spots. It could have run into the early eighties, but I was in High School by then and didn't watch much Saturday morning cartoons anymore.
I had purchased the Schoolhouse Rock VHS tape awhile ago and recently upgraded to the DVD, which is owned by Disney now. I played them often for our kids. My youngest was having trouble with her multiplication of fours in school this past year, no matter what my wife did to tutor her it didn't help her. I played "Four Legged Zoo," and had my daughter watch it over and over, until the song was "in her head." She got a 100% on her test that week.
The "I'm Just a Bill" spot was great in explaining how a bill gets passed into a law in Washington. My wife's favorite spot was Conjuction Junction, she was always big on the English Composition stuff.
My favorites were the history spots, At that time the USA was coming up on the Bi-centennial and there was a lot of patriotic saturation in the schools and on TV, I remember.