“Mother: What did you learn in school today? Son: Not enough. I have to go back tomorrow.”

An old joke has a parent ask a child about the day in school:
 
Mother: What did you learn in school today?
Son: Not enough. I have to go back tomorrow.
 
The joke has been cited in print since at least 1918, when it was printed in many newspapers.
 
   
23 January 1918, Kansas City (MO) Star, pg. 14, col. 2:
Call Again.
From the Indianapolis News.
The young “pride of the family” had been to school for the first time in his short six years.
 
“What did you learn?” asked his mother, as mothers always ask one the afternoon after the morning before.
 
Little Johnny frowned.
 
“I didn’t learn nothin’,” he replied. “I have to go back tomorrow.”
 
Chronicling America
14 February 1918, Hope (ND) Pioneer, pg. 5, col. 1:
Call Again.
The young “pride of the family” had been to school for the first time in his short six years.
 
“What did you learn?” asked his mother, as mothers always ask one the afternoon after the morning before.
 
Little Johnny frowned.
 
“I didn’t learn nothin’,” he replied. “I have to go back tomorrow.”
 
18 October 1946, San Diego (CA) Union, “Northeast Corner,” pg. 2-B, col. 8:
ANYWAY, MANY kids have an attitude toward school like that of the youngster who came home from her first day of school.
 
“Well, dear,” said her mother, “what did you learn in school today?”
 
“Not much,” she replied. “I have to go back tomorrow.”
 
Google Books
A Treasury of Mom, Pop, & Kids’ Humor
By James E. Myers
Springfield, IL: Lincoln-Herndon Press
1997
Pg. 209:
lt was Elmer’s first day ever in school, and when he came home his mother asked, “What did you learn in school today, Elmer?”
 
Elmer replied: “Not enough, Mom. l got to go back tomorrow.”
   
Google Books
April 1999, Boys’ Life, “Think & Grin,” pg. 61, col. 3:
A boy came home from his first day of kindergarten and his mom asked him, “What did you learn in school today?”
 
The boy replied, “Not enough because they want me to go back tomorrow!
—Nick Barrow, Clarksville, Tenn.
 
Google Books
696 Silly School Jokes & Riddles
By Joseph Rosenbloom
New York, NY: Sterling Publishing Company, Inc.
2003
Pg. 12:
WHAT DID YOU LEARN IN SCHOOL TODAY?
MOTHER: What did you learn in school today?
AUDREY: Not enough. I have to go back tomorrow.
 
Google Books
A Tribute to Teachers:
Wit and Wisdom, Information and Inspiration about Those Who Change Our Lives
By Richard Lederer
Portland, OR: Marion Street Press
2011
Pg. ?:
Another kindergartener came home from his first school day, and his mother asked him, “What did you learn in school today?”
 
“Not enough,” replied the little boy. “They say I have to go back tomorrow.”
   
Google Books
The Mammoth Book of One-Liners
By Geoff Tibballs
London: Constable & Robinson
2012
Pg. ?:
Mother: “What did you learn in school today?”
Son: “Not enough. I have to go back tomorrow.”