You're a Good Man, Charlie Brown has a few songs that have become somewhat familiar, though the only one that really "broke out" was "Happiness." In large part that's because the songs -- written by Clark Gesner -- are "book" numbers, those which are case-specific to the story and don't really lend themselves to a life outside of the show.
This is one of those book songs, and it's also one of the lesser-known ones, more a dramatic quartet than a traditional song -- and one of my favorites. It's "The Book Report," which wonderfully follows the horrors that little kids feel when given a Big Homework Assignment, and the lengths they'll go to somehow finagle their way around it, often thinking that they're tricking the teacher. It's so insightful, and whimsical, and richly musical, focusing on four of the characters signing in counterpoint.
This comes from the 1973 television adaptation of the musical, that used the animated characters rather than the adult actors of the Broadway show.