Sometime in the early 1970s (best guess, 1971-1972) trombonist Urbie Green made a promotional film for King Musical Instruments, giving a clinic to students from Willowbrook High School and filmed at Proviso West High School, in the Chicago suburbs not far from where I grew up.
The clinic covers basic trombone technique mostly, but he also covers some more advanced multiple tonguing and slide techniques. Throughout the whole video Urbie demonstrates and performs for the students, which alone would make this video worth watching.
Check out both parts:
