“Why did the Cyclops give up teaching?”/“He only had one pupil.”

A Cyclops riddle is:
 
Q: Why did the Cyclops give up teaching?
A: He only had one pupil.
 
The joke has been cited in print since at least 1980.
 
“Why did the cross-eyed teacher lose her job?”/“She couldn’t control her pupils” is a similar joke.
 
 
Wikipedia: Cyclops
A Cyclops (/ˈsaɪklɒps/ sy-klops; Ancient Greek: Κύκλωψ, Kuklōps; plural cyclopes /saɪˈkloʊpiːz/ sy-kloh-peez; Ancient Greek: Κύκλωπες, Kuklōpes), in Greek mythology and later Roman mythology, was a member of a primordial race of giants, each with a single eye in the center of his forehead. The word “cyclops” literally means “round-eyed” or “circle-eyed”.
       
8 May 1980, Lexington (KY) Herald, Whatchamacallit sec., pg. 1, col. 5:   
Why did the cyclops have to close his school? Because he had only one pupil!
 
17 January 1982, Newsday (Long Island, NY), “Smiles,” Kidsday, pg. J9, col. 3:
Why did the cyclops close to the school?
Because he had only one pupil.
—Brian Kelty, Mastic Beach
 
27 November 1983, The Sun-Herald (Sydney, Australia),  “Ha-Ha-Ha,” pg. 93, col. 5:
Q: Why did the Cyclops have to close his school?
A: He’d only got one pupil.
Deborah (14), Dover St, Marsfield.
 
4 August 1985, Newsday (Long Island, NY), “Smiles,” Kidsday, pg. SM39, col. 3:
Why did the Cyclops have to close his school?
He had only one pupil.
—Michael Melman, Plainview
 
Google Groups: alt.mythology
Cyclops Sites? 
PSmith9626
4/2/99
(...)
All the teachers on cyclops island are very happy, no matter how many students in a class they all have only one pupil.—penny
   
5 October 1999, Los Angeles (CA) Times, “The Kids’ Reading Room; Reading by 9; Pint-Sized Punch Lines,” pg. 7:
Why did the Cyclops close his school? Because he only had one pupil. (Ian, 9, Wichita, Kan., Beech Elementary)
 
Google Groups: alt.teens.penpals
Scholastics.
merry mcgrath
10/9/99
Why did the Cyclops close down his school?  Because he only had one pupil.
 
Google Groups: alt.humor.puns
Puns of the Weak 10/19/01
Stan Kegel
10/20/01
(...)
Why did the Cyclops close his school? He had only one pupil! (Syman and McNair)
 
Google Groups: alt.humor.puns
Puns of the Weak 11/09/01
Stan Kegel
11/10/01
(...)
Why did the Cyclops close his school?
He had only one pupil!  (The Daily Groaner)
 
8 March 2002, Los Angeles (CA) ,Times, “The Kids’ Reading Room; Reading by 9; Jokes & Riddles,” pg. E7:
Why did the Cyclops stop teaching? He only had one pupil. (Arturo, sixth grade, Porter Middle School, Granada Hills)
     
Google Books
The Everything Kids’ Gross Jokes Book:
Side-splitting jokes that make your skin crawl!
By Aileen Weintraub
Avon, MA: Adams Media
2005
Pg. ?:
Why was the Cyclops such an attentive teacher?
He only had one pupil. kids?
 
Google Books
The Great Monster Joke Book
By Amanda Li
New York, NY: Puffin Books
2006
Pg. ?:
Why did Cyclops give up teaching?
He only had one pupil.
 
Twitter
Ola Claesson
‏@Ola_Claesson
Why did the Cyclops give up teaching? He only had one pupil! It´s so bad it´s good.
8:22 AM - 5 Sep 2008
 
Twitter
Oly Grocery Outlet
‏@OlympiaGO
Bad Joke of the Day: Why did the cyclops give up teaching? Because he only had one pupil!
10:53 AM - 10 Jul 2009
 
Google Books
Jokelopedia:
The Biggest, Best, Silliest, Dumbest Joke Book Ever!
Compiled by Eva Blank, Alison Benjamin, Rosanne Green, Ilana Weitzman and Lisa Sparks
New York, NY: Workman Publishing
2013
Pg. ?:
Why did the cyclops have to close his school?
Because he had only one pupil.
 
Google Books
More Halloween Jokes For Kids
By Peter Crumpton
PeteyRF Creative
2015
Pg. ?:
Why did the cyclops stop teaching?
Because he only had one pupil!