Found in this tweet by @MarkRPriestley.
My link is to a pdf of the talk from 1969. Now seem broken so archive.org
Postman also wrote kairosschool.co.za/wp-content/uploads/2011/02/Teaching-as-a-Subversive-Activity.pdf.
A good fun read with many cringe points, which of the forms of BS have you used? I’ve used a lot.