In addition to what was an on-again, off-again tradition of airing a half-hour sneak preview special on the eve of the cartoon season, ABC in 1973 thought it might be a good idea to devote some in-house ad space to give parents a heads-up about their children's programming slate for the coming season. To tell you the honest truth, I never saw this ad until now.
Actor Michael Constantine (Room 222) is the speaker in this spot, uploaded by RetroGoop. Note that Schoolhouse Rock was listed as Scholastic Rock at the top of the list. Seems Scholastic Books was claiming copyright infringement or somesuch, hence the change to the iconic title we'd all come to love.
Edit, 2/15/18: RetroGoop's account apparently has been discontinued, and the video has been deleted by YouTube. Sorry 'bout that.
This year, ABC is going with an all-live-action lineup to fulfull FCC E/I requirements, as they're making the same experimental move that NBC made nearly 20 years ago in excising cartoons from their Saturday slate. That lineup goes into effect on September 3, getting a headstart on the other networks. Now, don't ya think they'll be getting letters from irate kids who wanted to see Phineas & Ferb instead of Jack Hanna's new animal show? We'll see.