If you've never heard of this song before, that's because: 1) "Schoolboy Blues" is actually an alternate title for the song. 2) The song was never released anyway. The reason for both becomes obvious when you read the song's lyrics and its original, uncensored title: "Cocksucker Blues."
This song came about as the Stones were set to establish their own record label. They had one single left to record for their old label (Decca) in order to fulfill the terms of their contract, and this was it. It was a kiss-off to the label, who retaliated by releasing a compilation album called Stone Age, which the band denounced in full-page ads placed British music magazines. The album still made #4 on the UK chart.
With "Schoolboy Blues" the Rolling Stones apparently took a cue from Phil Spector, who in 1963 wrote and had the Crystals record "(Let's Dance) The Screw" as a parting shot at Lester Sill, his former partner at Philles Records, with whom Spector had had a falling-out. (A persistent myth is that "The Screw" was also meant to technically fulfill the terms of a contract, but Sill has denied this).
Although Decca never released this single, the song did appear as part of the original West German release of the boxed set The Rest of the Best, but after 4 weeks the set was re-issued without this song.
Suggestion credit: Joshua - Twin Cities, MN, for all above