"We'll never run out of math teachers because…

“We’ll never run out of math teachers because they always multiply” is a jocular one-line saying that has been printed on several images. The math pun has been cited in print since at least January 2007.

Google Groups: rec.crafts.textiles.needlework
OT-Puns for the Punny
Lucille
1/15/07
(...)
>>>> >* We’ll never run out of math teachers because they always multiply.

19 January 2007, Pensacola (FL) News Journal, “Just Awful Jokes,” pg. 3B, col. 3:
We’ll never run out of math teachers because they always multiply.

18 February 2007, Edmonton (Alberta) Journal, “Why Barney tunes get stuck in your head” by Terry McConnell, pg. E2:
We’ll never run out of math teachers because they always multiply.

Twitter
Don Myers‏
@azthumper
We’ll never run out of math teachers, because they always multiply! lol
1:48 PM - 8 Apr 2009

Google Books
Teaching Language Arts to English Language Learners
By Anete Vásquez, Angela L. Hansen and Philip C. Smith
New York, NY: Routledge
2010
Pg. ?:
We’ll never run out of math teachers because they always ______. (multiply)

Google Books
The Laugh-a-Day Book of Bloopers, Quotes & Good Clean Jokes
By Jim Kraus
Grand Rapids, MI: Revell
2012
Pg. ? (Day 68):
We’ll never run out of math teachers because they always multiply.

Twitter
Miss Lynch’s Class‏
@mramathletes
Why don’t we ever run out of math teachers? Because they multiply!!! Have a Factoring Friday Mathletes!
6:00 AM - 25 Aug 2017

Twitter
sho ⚔️‏
@shoreadytofight
we’ll never run out of math teachers because they always multiply ⚔️🗡⚔️
10:37 PM - 23 Jan 2018