“What is the king of the classroom?”/“The ruler.”

A riddle about an object found in schools is:
 
Q: What/Who is king of the classroom?
A: The ruler.
 
The riddle has been cited in print since at least 2005.
 
     
2 March 2005, Los Angeles (CA) Times, “The Kids’ Reading Room: Jokes & Riddles,” pg. E15, col. 4:
What is king of the classroom? The ruler.
Mouradian, 11
Los Feliz Elementary
Los Angeles
   
6 June 2005, Star-Tribune (Minneapolis, MN), “Mindworks: Favorite Jokes,” pg. 1E:
Who is the king of the classroom?
A ruler.
Tiana Raimist-Carter, 7
Minneapolis
Marcy Open School
 
Google Books
February 2008, Boys’ Life, “Think & Grin,” pg. 52, col. 2:
Joe: What’s the king of all school supplies?
Moe: I don’t know. What?
Joe: The ruler.
Connor Bennett, Metairie, La.
 
Twitter
Prongo kids games
‏@Prongo
Joke of the Day: Q: Which object is king of the classroom? A: The Ruler Submitted by: Elizabeth:  #jokes #comedy
1:42 PM - 25 May 2009
 
Google Books
Jokes about School
By Judy A. Winter
Mankato, MN: Capstone Press
2011
Pg. ?:
What is the king of the classroom?
The ruler.
 
Google Books
nsults Anywhere Kids Presents
Hundreds Of Kids Jokes They Can Tell Anywhere!
By Franklin Yantz
Insults Anywhere
2014
Pg. ?:
Q: What object is king of the classroom?
A: The ruler!
 
Google Books
111 LOL Jokes About School & Wimpy Teachers!:
Jokes, Riddles and Crazy Excuses for Avoiding Homework!
By Marcus Stuart, Sir Laughs A. Lot
LOL Kids Books
2015
Pg. ?:
What object is king of the classroom?
The ruler!