TV producer Alan Sachs wanted a Lovin' Spoonful-like theme song for a new ABC sitcom entitled Kotter. Sachs' agent, Dave Bendet, also represented Sebastian and arranged for a meeting between the two. The producers liked the song so much that they changed the name of the series to Welcome Back, Kotter. Co-produced by Steve Barri and Sebastian, the song eventually sold over one million copies.
The song originally had one verse, meant for the TV series. Because of the popularity of the show, Welcome Back, Kotter, Sebastian, in the single version, added a second verse to the song, as well as an instrumental section featuring Sebastian's harmonica solo, before he resumes finishing up the verse, as well as the repeated chorus and coda to finish the song. The single version would eventually be used during the closing credits of Welcome Back, Kotter.