Throughout the whole special, Schroeder's Piano changes color numerous times.
While Charlie Brown, Pig Pen, and Snoopy sound perfectly fine without Schroeder when demonstrating their rock band to Lucy, they aren't able to go on without him at the PTA meeting.
When Charlie Brown, Snoopy, and Pigpen yell "Forget It! Augggh!," They were accidentally voiced by Pamelyn Ferdin.