From the recording Concert Music
This is the only cut on the album with guitar on it. Sort of a demented Freddie Green thing going. Andrew's Trombone Lesson is from a MASH episode wherein Henry Blake is handling multiple crises: there in Korea and back in Bloomington Illinois The home crisis involves Andrew's Trombone Lesson. As far as what that has to do with the music, your guess is as good as mine. But that's where the title came from.