“School is a building that has four walls—with tomorrow inside” is a frequently cited one-line saying about school. “What is a School?” is a eulogy that was written by Dan Valentine and reprinted in the September 5, 1967, Salt Lake Tribune (Salt Lake City, UT). The first line was: “A school is a building of four walls…with tomorrow inside.”
 
The aphorism has been credited to “Lon Watters” (or “Lon Waters” or “Lon Walters”) since the 1980s, but it’s probable that this person used Dan Valentine’s words and has received improper credit.
   
 
5 September 1967, Salt Lake Tribune (Salt Lake City, UT), “Dan Valentine’s Nothing Serious,” pg. B7:
WHAT IS A SCHOOL?
A SCHOOL IS A BUILDING of four walls…with tomorrow inside.
(This is a reprint of a “eulogy” that Valentine wrote “several years ago,” according to the newspaper—ed.)
 
30 August 1968, Corona (CA) Daily Independent,  “Getting the teachers cranked up” by Bette Reincke, pg. 3, col. 1:
And, “A school is a building of four walls…with tomorrow inside.”
 
15 November 1973, Spirit Lake (IA) Beacon, ‘What Is A School?” by Deb Goetsch, pg. 4, col. 2:
I recently found a story that expressed my thoughts and feelings of what a school is, and maybe it will be the same for you. The story is by Dan Valentine, and it is originally meant for elementary, but the meaning and thoughts are about the same for any type of school.
 
A SCHOOL IS A BUILDING of four walls…with tomorrow inside.
   
Google News Archive
29 December 1982, Cold Spring (MN) Record,  “Community Action Center” by Bill Goede, pg. 10, col. 3:
WORDS FOR THE WEEK —“School is a building that has four walls — with tomorrow inside.”—Lon Walters.
 
17 July 1983, Marietta (GA) Daily Journal,  “Backstairs At The White House” by Helen Thomas, pg. 5A, col. 1:
“Someone once said that a school is a building that has four walls and tomorrow inside.”
(President Ronald Reagan—ed.)
   
2 September 1984, Seattle (WA) Times, “Best, worst of times: Tale of 2 teachers” by Constantine Angelos and Sally Macdonald, pg. A23, col. 4:
In her classroom, Wiggins displays a poster that says it all: “A classroom is four walls with tomorrow inside.”
     
Google News Archive
28 August 1986, Courtland (KS) Journal, “First Day Of School Sparks Many Memories” by Grandma Sez, pg. 1, col. 3:
Our schools are buildings of four walls or more — with tomorrow inside.
 
OCLC WorldCat record
Four walls with tomorrow inside : a book to honor teachers by placing the “Pal” back into “Principal”
Author: Scott Ober
Publisher: [Philadelphia, PA] : Xlibris, ©2002.
Edition/Format:   Book : English
   
Google Books
Thank You, Teacher:
A collection of poems, prayers, stories, quotes and scriptures to say thank you
By Caron Loveless; Between the Lines (Group)
West Monroe, LA: Howard Publishing
2003
Pg. ?:
School is a building that has four walls — with tomorrow inside. LON WATTERS