Charlie Mingus question

Hi all, I'm trying to find a source for the following story. Charlie Mingus had some serious issues about free jazz to say the least. At one show he presented, a band was playing some 'free' music behind a screen. He lifted the screen away to later reveal that it was a group of children learning to play their instruments. All done to make a point obviously. Does anyone know a source for this story? I seem to remember reading this in a jazz book but I can't find this now. Thanks in advance for any help with this, Jason Perfect Sound Forever online music magazine with warped perspectives since 1993 http://www.perfectsoundforever.com