Nelson Mandela (1918-2013) often stressed the importance of education. “Education is the most powerful weapon which you can use to change the world” is a popular Mandela quote that was made in June 1990, during a visit to a Massachusetts school. “Education is the most powerful weapon we can use to change the world” was said by Mandela in 2003.
 
“Education is the most powerful weapon” had been used earlier, in 1910, 1931, 1951, 1957 and 1964.
   
 
Wikipedia: Nelson Mandela
Nelson Rolihlahla Mandela (Xhosa pronunciation: [xoˈliːɬaɬa manˈdeːla]; 18 July 1918 – 5 December 2013) was a South African anti-apartheid revolutionary as well as a politician and philanthropist who served as President of South Africa from 1994 to 1999. He was the first black South African to hold the office, and the first elected in a fully representative election. His government focused on dismantling the legacy of apartheid through tackling institutionalised racism, poverty and inequality, and fostering racial reconciliation. Politically an African nationalist and democratic socialist, he served as the President of the African National Congress (ANC) from 1991 to 1997. Internationally, Mandela was the Secretary General of the Non-Aligned Movement from 1998 to 1999.
     
1 April 1910, Watertown (NY) Daily Times, “Will Organize a Chautaugua Circle,” pg. 5, col. 2:
Education is the most powerful weapon at the command of the American Jew.
 
20 November 1931, Oak Park (IL) Oak Leaves, pg. 31:
Moral education is the most powerful weapon we have to combat the complexities of modern life.
 
24 March 1951, Morning Advocate (Baton Rouge, LA), pg. 5-A, col. 6:
Says Education Is Best Weapon For Defense
Biloxi, Miss., March 23 (AP)—A Tulane university professor of physics said here that education is the most powerful weapon for defense the United States has today.
 
30 October 1957, Springfield (MA) Union, “Dr. Merriam Speaks at Ward 8 Meeting,” pg. 27, col. 1:
Emphasizing the statement made to the Hampden County Teachers Association by U.S. Commissioner of Education Lawrence G. Derthick last Friday that education “is the most powerful weapon in freedom’s armory,” Dr. Merriam advocates a 10-year building program for Springfield schools.
 
27 November 1964, Trenton (NJ) Evening Times, “Education, Mightiest Weapon: Diplomat Turns Again To Teaching,” pg. 29, col. 5:
‘After 28 years of teaching and five years of diplomatic service, I feel education is the most powerful weapon for the improvement of international and race relations,” Dr. Morrow (Dr. John H. Morrow—ed.) says.
   
24 June 1990, The Orange County Register (Santa Ana, CA), “Boston embrace Mandela in daylong show of unity” by Peter j. Howe and Diane E. Lewis (The Boston Globe), pg. A6, col. 4:
Earlier, Mandela urged Roxbury schoolchildren to do everything they could to stay in school, saying, “Education is the most powerful weapon which you can use” to change the world.
 
Google Books
“We respect you ; we admire you ; most of all, we love you.”:
June, 1990, Nelson Mandela—African National Congress (A.N.C.) tour in the United States press clips
By Mozambique Support Network.
Chicago, IL: Mozambique Support Network
1990
Pg. ?:
Earlier, Mandela urged Roxbury schoolchildren to do everything they could to stay in school, saying, “Education is the most powerful weapon which you can use” to change the world.
   
Nelson Mandela Centre of Memory
Nelson Mandela Foundation
Title: Lighting your way to a better future
Sub-title: Speech delivered by Mr N R Mandela at launch of Mindset Network
Presentation(s)
Occasion: Launch of Mindset Network
Place: Planetarium, University of the Witwatersrand Johannesburg South Africa
Date:  Wednesday, July 16, 2003
Transcript
(...)
Education is the most powerful weapon we can use to change the world and Mindset Network is a powerful part of that world changing arsenal.
 
Google Books
Oxford Treasury of Sayings and Quotations
By Susan Ratcliffe
New York, NY: Oxford University Press
2011
Pg. 137:
Education is the most powerful weapon which you can use to change the world.
Nelson Mandela 1918– :speech, Madison Park High School, Boston, 23 June 1990; reported in various forms including “...weapon which you can use in order to prepare our youth for their role as leaders of tomorrow” on CBS News 23 June 1990 and “...weapon we will need” in New York Times 24 June 1990