“What school do you have to drop out to graduate from?”/“Parachute school.”

A school riddle is:
 
Q: What school do you have to drop out to graduate from?
A: Parachute school.

 
The joke has been cited in print since at least 1972.
 
           
Google Books
August 1972, Boys’ Life, “Think and Grin,” pg. 66, co. 3:
Duke: Do you know one school where you have to drop out in order to graduate?
Luke: Parachute school. — Steve Suman, Kettering, Ohio
   
Google Books
Biggest Riddle Book in the World
By Joseph Rosenbloom
Illustrations by Joyce Behr
New York, NY: Sterling Publishing Company, Inc.
1976
Pg. 214:
In what school do you have to drop out in order to graduate?
Parachute school.
 
9 August 1982, Trenton (NJ) Times, “Is anybody ready for bocce marathon?” by Frank Tyger, pg. C1, col. 3:
Overheard at the Lawrence Shopping Center:
“Name one school where you have to drop out to graduate.”
“Parachute school.”
   
Google Groups: rec.humor
Life 4.D
Henry Cate III
5/6/93
(...)
Duke: Do you know one school where you have to drop out in order to graduate?
Luke: Parachute school.
   
17 August 1997, Newsday (Long Island, NY), Kidsday sec., pg. 1:
What school do you have to drop out of to graduate?
Parachute School.
- Stephen Pallas, Manorville
   
Twitter
zwiebelzwiebel1‏
@zwiebelzwiebel1
What kind of school do you have to drop out of to graduate? Answer: Parachute school!
8:56 AM - 6 Sep 2010
 
Twitter
Jimmy‏
@crashr
I was trying to graduate parachute school but I had to drop out.
6:47 PM - 19 Feb 2011
 
Twitter
suzicalisha‏
@Suzicalisha
What kind of school do you have to drop out of to graduate?  Parachute school! #BadJokeTuesday @TeamCoco @jimmyfallon @TheEllenShow
10:02 AM - 29 Mar 2011
 
Google Books
Awesome Jokes For Kids 7
By Peter Crumpton
PeteyRF Creative
2015
Pg. ?:
What school do you have to drop out of to graduate from?
Parachute school!
 
Twitter
Quick Funny Jokes‏
@quickfunnyjokes
At what school do you have to drop out so you can graduate? Parachute school! #SchoolJokes http://www.quickfunnyjokes.com/schoolteacher.html
7:33 PM - 5 Sep 2017