| Date | Event |
| 1902 | Ernest Coulter, court clerk, helps organize the first New York Children's Court; Ladies of Charity, later Catholic Big Sisters of New York, start to befriend girls who come before the New York Children's Court |
| 1903 | Businessman Irvin F. Westheimer befriends a young boy in Cincinnati, OH; seeds are formed for start of Big Brothers in Cincinnati |
| 1904 | Ernest Coulter founds the organized Big Brothers movement by obtaining 39 volunteers, who each agree to befriend one boy |
| 1912 | The New York Times reports Big Brothers activity in 26 cities |
| 1914 | Ernest Coulter embarks on nationwide lecture tour on behalf of Big Brothers; planning begins for a national Big Brothers and Big Sisters organization |
| 1916 | Big Brothers work has spread to 96 cities |
| 1917 | The first national conference of Big Brothers and Big Sisters organizations is held in Grand Rapids, MI., leading to the later organization of the Big Brothers and Big Sisters Federation |
| 1923 | Big Sisters work geared to African-Americans underway in Louisville, KY and Brooklyn, NY;
Theodore Roosevelt, Jr., becomes treasurer of the Big Brothers and Big Sisters Federation;
First motion picture based on a Big and Little Brother relationship released by Paramount Pictures |
| 1925 | BB/BSF holds its first conference for agency executives;
President Calvin Coolidge becomes patron of the Big Brothers and Big Sisters Federation |
| 1930 | Six hundred delegates attend a Big Brothers and Big Sisters Federation meeting in New York City on March 8 |
| 1934 | President and Mrs. Franklin D. Roosevelt become patrons of Big Brothers and Big Sisters Federation |
| 1940 | National Committee on Big Brothers and Big Sisters service is created to continue to pursue the formation of a national group |
| 1947 | Big Brothers Association headquarters opens in Philadelphia |
| 1948 | Norman Rockwell produces sketch that becomes a symbol for the Big Brothers Association |
| 1951 | Big Brothers of the Year Program begins, Associate Justice Tom Clark of the U.S. Supreme Court and J. Edgar Hoover are named |
| 1952 | Ernest Coulter dies |
| 1958 | Big Brothers Association is chartered by Congress |
| 1968 | Big Brothers Big Sisters of Central Iowa is founded in Des Moines |
| 1969 | Big Brothers Association grows to 150 affiliated agencies |
| 1970 | Big Sisters International is incorporated |
| 1971 | Big Brothers Association reports 208 affiliates |
| 1977 | Big Sisters International and Big Brothers Association merge, forming Big Brothers Big Sisters with 357 agencies |
| 1984 | Big Brothers Big Sisters of America occupies its new headquarters at 230 North 13th Street in Philadelphia |
| 1985 | Big Brothers Big Sisters of America is honored with a commemorative stamp by the Postmaster General |
| 1986 | Big Brothers Big Sisters begins long range governance planning process: creating standards and required procedures |
| 1989 | Public/Private Venture's begins study to gauge impact on youth of having a Big Brother or Sister |
| 1994 | Big Brothers Big Sisters kicks of Project 21st Century to develop mission and vision statements, goals and strategies;
"How-To" mentoring training developed |
| 1995 | Public/Private Venture's Study research shows measurable, positive results on youth who have a Big Brother or Sister; seminal research in the field of youth mentoring |
| 1997 | President William J. Clinton holds Volunteer Summit in Philadelphia, Big Brothers Big Sisters plays key role |
| 1998 | Big Brothers Big Sisters International is founded |
| 2000 | Big Brothers Big Sisters in Schools becomes a core program, partnerships with schools and volunteer-rich organizations such as churches, colleges, employers, and fraternities are emphasized, including the piloting of the Amachi Big Brothers Big Sisters program which matches children of prisoners with church congregants |
| 2001 | Brand New Thinking marketing program focuses on the shared experiences to broaden volunteer appeal and the tagline "Little Moments, Big Magic" is developed |
| 2002 | A consistent approach for providing services to children at all agencies is created to increase Big Brothers Big Sisters’ ability to offer quality services to greater numbers of youth |
| 2003 | President George W. Bush announces three-year $450 million mentoring initiative in State of the Union Address |
| 2004 | Big Brothers Big Sisters celebrates 100 years of serving America’s youth |
| 2006 | First Lady Laura Bush stars in a public service announcement to recruit volunteers across the nation |