“What do Santa’s elves learn at school?”/“The elfabet.”

A Christmas riddle is:
 
Q: What do Santa’s elves learn at school?
A: The elfabet.
       
The “elfabet” (elf + alphabet) pun was posted on the newsgroup rec.humor on November 26, 1999. The riddle has been printed on several images.
   
 
Google Groups: rec.humor
What do Santa’s elves learn in school?
Merv
11/26/99
What do Santa’s elves learn in school?
The elfabet.
 
24 December 2000, Yakima (WA) Herald-Republic, “Christmas Cheer Put Into Print” by Sarah Jenkins, pg. E1:
Q. What do elves learn in school?
A. The elfabet.
     
Google Groups: alt.humor.puns
Puns of the Weak 01-09-04 Part 2 The Short Puns
Stan Kegel
1/10/04
(...)
What do elves learn at school?
The elf-abet! (Kiran, 11)
   
Google Books
Mind Knots:
A Book of Riddles
By Mark Ziegler
Minneapolis, MN: Picture Window Books
2006
Pg. 18:
What do elves learn in school?
The elfabet.
   
Google Books
Penguin Pocket Jokes
By David Pickering
London, UK: Penguin Books
2006
Pg. ?:
What do elves learn at school?
The elfabet.
 
Twitter
Prongo kids games‏
@Prongo
What does an elf learn in school? answer- the elfabet
11:04 AM - 1 Jul 2009
 
Google Books
Horrid Henry’s Jumbo Joke Book (3-in-1)
By Francesca Simon
London, UK Orion Children’s Books
2015
Pg. ?:
What do elves learn at school?
The Elfabet.
 
PopSugar
25 Holiday Jokes That Will Make Your Kids Belly-Laugh Like Santa
December 6, 2017 by DANA ZEPEDA
(...)
1. “What do Santa’s elves learn at school?” Answer: “The Elfabet.”