Damn frustrating too, having a missing piece. School shut down in 1991 and that piano teacher’s not in the yearbook. I know it can’t have been a style of improvisational composition invented after 1986/7.
So now I just tracked down a copy of John Cage: “Notations”, 1969. It’s got to be in there. I’ll be REALLY pissed if it’s just that music teacher’s own ‘thing’.