I found a b&w clip on YouTube aired in 1976, English - lesson 54. It's definitely Telekolleg I, at least the accompanying books are titled like that. There are probably 78 lessons. At least aired since May 1967. Oldest books (TR-Verlagsunion) I found were published in 1969.
Telekolleg I (1982) in color (Englisch für Anfänger), host Graham Pascoe was very famous. I had him in Auffrischungskurs Englisch (abridged, 1996)
I'm a bit confused as I found Telekolleg II books claiming to be published in 1973 (why is Telekolleg I then 1982? A 1977 edition is about the 1982 course). I'm also not sure about the host here. Follow Me (host Francis Matthews, BBC) was in 1978 and already in color.
There was also Telekolleg II and related series. Telekolleg is ELT for adults. So not School TV anyway. This one aired in Switzerland but Telekolleg first aired in German from bradcaster BR.
https://schulfernsehenenglischhistory.blogspot.com/2021/08/telekolleg.html
https://schulfernsehenenglischhistory.blogspot.com/2021/07/chronological-list.html