“There are three good reasons to be a teacher: June, July and August”

“There are three good reasons to be a teacher: June, July and August” is an old joke about the teaching profession, perhaps outdated for teachers who work in June. “Three good reasons for being a teacher—June, July and August” has been cited in print from at least July 1962.
 
   
16 July 1962, Salt Lake Tribune (Salt Lake City, UT), “Monday Morning Go-Round,” pg. 18, col. 6:
Three good reasons for being a teacher—June, July and August.—New Mexico School Review, Santa Fe.
 
Google News Archive
26 July 1962, St. Marys (WV) Oracle, “Pleasantries,” pg. 4, col. 2:
Neighbor George Cox says there are three nice things about being a teacher: June, July and August.
 
18 November 1962, Marietta (GA) Daily Journal, pg. 19A, col. 7:
SHORT AND SWEET
NEW YORK (UPI)—A teacher asked for three good reasons for entering her profession, responded in a survey: “June, July and August.”
 
15 April 1970, Aberdeen (SD) American-News, “Earl Wilson’s New York,” pg. 5, col. 5:
EARL’S PEARLS: Asked for three reasons why she’d become a teacher, the lady said, “June, July and August.”
 
Google Books
May 1970, Boys’ Life, “Think & Grin,” pg. 82, col. 4:
Filling out a series of reports at the end of the school year, one tired teacher came upon this question, “List three reasons for entering the teaching profession.” Without hesitation she wrote, “June, July and August.”—Ronald Allen, Perryville, Mo.
 
Google Books
The End of Culture:
Essays on sensibility in contemporary society
By Kingsley Widmer
San Diego, CA: San Diego State University Press
1975
Though not as honestly cynical as the friend who listed three reasons for becoming a professor — namely, June, July and August (and when pressed for more reasons, added Tuesday and Thursday) — many colleagues’ ideal campus tells the story: ...
   
Time magazine
Education: Tough Guy for a Tough Town
By Ezra Bowen;John E. Gallagher/New York and Marc Hequet/Minneapolis Monday, Jan. 18, 1988
(...)
Says a high school teacher: “The three best things about the job are June, July and August.”
   
Google Books
The United States of Incompetence
By Art Carey
Boston, MA: Houghton Mifflin
1991
Pg. 99:
Many people become teachers, the old saw goes, for three reasons — June, July, and August — and also because the job is secure, largely free from accountability, and, if not taken seriously, relatively easy.
   
22 June 2003, Sacramento (CA) Bee, “Summer Vocations: Roseville high school district teachers expand their horizons,” pg. N1:
There’s an old joke, told by those who grade papers and suffer unruly students, that there are three good reasons to be a teacher: June, July and August.