“Why do fish swim in schools?”/“Because they can’t walk in schools.”

A school riddle is:
 
Q: Why do fish swim in schools?
A: Because they can’t walk in schools.
 
The joke has been cited in print since at least 2004. when it was printed on a Laffy Taffy wrapper.
 
             
comoonplacebook.com
Laffy Taffy Jokes (the worst jokes in the world)
Posted on February 18, 2004 by Hawthorn Mineart
(...)
Why do fish swim in schools? — Because they can’t walk in schools.
 
Mastermelanie
LAFFY TAFFY
monday, 19 july, 2004 23:20 MAT
(...)
Q: why do fish swim in schools?
A: because they can’t walk in schools.
 
Twitter
Lora B‏
@Lora
laffytaffy wrapper joke: why do fish swim in schools?  because they can’t walk in schools.  Who writes this stuff?
9:19 AM - 28 Feb 2008
 
Google Books
March 2009, Boys’ Life, “Think & Grin,” pg. 55, col. 3:
Jaylun: Why do fish swim in schools?
Ray: I don’t know.
Jaylun: Because they can’t walk!
Jaylun Robinson, Greensboro, N.C.
   
Google Books
Just Jokes a Collection of Kids Jokes
By Phyllis Agles-Johnson
Raleigh, NC: LULU Publishing
2010
Pg. 71:
Q. Why do fish swim in schools?
A. Because they can’t WALK in schools!
   
Facebook
Interskate South
September 1, 2015 ·
Laffy Taffy Joke of the Day: Why do fish swim in schools?
Because they can’t walk in schools.
 
Twitter
dad jokes‏
@dadtellsjokes
Why do fish swim in schools? Because they can’t walk in schools.
7:15 PM - 30 Jan 2018