Was it, 'I Want Candy' by the Bow Wow Wow's, or "Video Killed the Radio Star" by the Buggles? How about 'Ride Captain Ride on Your Mystery Ship' by the Blue Images or 'In A Big Country' by who else, Big Country?
Nope, it wasn't.
Of all the one hit wonders to ever hit big, To Kill a Mockingbird by Harper Lee was clearly the biggest of big. Since it's publication in the 1960's Ms. Lee's book has sold well over 30 million copies. 30 Million. Can you imagine? And if you check Amazon it's in the top 2000 books right now. (If my book spikes at 2000 for an instant I'll fall over, apoplectic.)
I finished it for the second time in several years (the first time being in middle school which was... like I said several years) and really appreciated it more now than I did then. I can see why I was made to read it. It's elegant, understated, and emensly powerful. I don't need to run through a critique, there are 50 years worth of those. If you haven't read it since you were made to do so as a kid, then you should revisit. In spite of the blantant racism, the adult content that I didn't catch when I wasn't an adult (for instance, the accusation of incest that Tom R obliquely makes against the little terd Ewell- do you remember it? If not that's what I mean) it's still great both in spite of and because of, for different reasons.
As far as a one-hit wonder (Ms Lee never published another book) I am reminded of a quote from Joe Heller I once read. Paraphrasing: An interviewer noted that in his subsequent writing Heller had never written anything as good as Catch-22. He replied that the interviewer (nor most people that write) had never written ANYTHING as good ever.