Title: Harvard Crimson football
Content:  Since the formation of the Ivy League in 1956, Harvard has won outright or shared 17 Ivy League championships (8 outright; 9 shared), 1961 (6–3), 1966 (8–1), 1968 (8–0–1), 1974 (7–2), 1975 (7–2), 1982 (7–3), 1983 (6–2–2), 1987 (8–2), 1997 (9–1), 2001 (9–0), 2004 (10–0), 2007 (8–2), 2008 (9–1), 2011 (9–1), 2013 (9–1), 2014 (10–0) and 2015 (9–1). The Crimson are behind Penn and Dartmouth's 18 Ivy League Football Championships. In summer 2020, the Ivy League announced that the fall season would be postponed or even cancelled because of the COVID-19 pandemic. Play did not resume until September 2021, after a nearly two-year hiatus, with a 44-9 victory over Georgetown.
Title: Harvard Crimson women's basketball
Content:  Harvard has won the Ivy League eleven times, with four shared (1986, 1988, 2005, and 2008) and seven won outright (1991, 1996, 1997, 1998, 2002, 2003, and 2007). Harvard has lost twice in a playoff to determine the automatic bid to the NCAA Tournament, losing 75–61 to Dartmouth in 2005 and losing to Dartmouth 68–62 in 2008.
Title: Kathy Delaney-Smith
Content:  to the tournament. The Ivy League would be granted an automatic bid starting in 1994. While an Ivy League team could be invited to the NCAA tournament as an at-large team, it has only happened once, by Dartmouth in 1983. Harvard finished first in the Ivy League in 1986, 1988, and 1991, but did not get their first invitation to the NCAA tournament until 1996. Harvard first played in an NCAA tournament in 1996. Although they lost to Vanderbilt, they hit 16 three-point attempts in the game, setting a record for an NCAA tournament game that has been subsequently tied but 
Title: Harvard Crimson football
Content:  Harvard has won 17 conference championships, all of which occurring during their tenure in the Ivy League, which they joined in 1956, with eight of them being outright and nine being shared. They are second in total Ivy League football titles, behind Dartmouth and Penn. † Co-championship
Title: Harvard Crimson men's soccer
Content:  Harvard has won 13 Ivy League championships. The Ivy League began sponsoring men's varsity soccer in 1955. Prior to 1955, Harvard competed as an Independent.
Title: Ivy League
Content:  bid, then rebounded to win outright championships in 2012, 2013, and 2014. Harvard also won the 2013 Great Alaska Shootout, defeating TCU to become the only Ivy League school to win the now-defunct tournament. Rivalries exist between other Ivy league teams in other sports, including Cornell and Harvard in hockey, Harvard and Princeton in swimming, and Harvard and Penn in football (Penn and Harvard have won 28 Ivy League Football Championships since 1982, Penn-16; Harvard-12). During that time Penn has had 8 undefeated Ivy League Football Championships and Harvard has had 6 undefeated Ivy League Football Championships. In men's lacrosse, Cornell and Princeton are perennial rivals, and they are two of three Ivy League teams to have won the NCAA tournament. In 2009, the Big Red and Tigers 
Title: 2013–14 Ivy League men's basketball season
Content:  among Ivy League members. The tradition began when the league was formed during the 1956–57 season and its history extends to the predecessor Eastern Intercollegiate Basketball League, which was formed in 1902. Harvard won the regular season title outright and earned the conference's only 2014 NCAA Men's Division I Basketball Tournament bid. Overall, the conference had five postseason participants and won eight postseason games, marking the best postseason in league history. Wesley Saunders of Harvard was named Ivy League Men's Basketball Player of the Year. James Jones of Yale was named Ivy League Coach of the Year and Spencer Weisz of Princeton was named Ivy League Freshman of the Year. Brown's Cedric Kuakumensah earned his second 
Title: Harvard University
Content:  Harvard University is a private Ivy League research university in Cambridge, Massachusetts. Founded in 1636 as Harvard College and named for its first benefactor, the Puritan clergyman John Harvard, it is the oldest institution of higher learning in the United States and among the most prestigious in the world. The Massachusetts colonial legislature authorized Harvard's founding, "dreading to leave an illiterate ministry to the churches, when our present ministers shall lie in the dust"; though never formally affiliated with any denomination, in its early years Harvard College primarily trained Congregational clergy. Its curriculum and student body were gradually secularized during the 18th 
Title: Harvard College
Content:  Harvard College is the undergraduate college of Harvard University, an Ivy League research university in Cambridge, Massachusetts. Founded in 1636, Harvard College is the original school of Harvard University, the oldest institution of higher learning in the United States and among the most prestigious in the world. Part of the Faculty of Arts and Sciences, Harvard College is Harvard University's traditional undergraduate program, offering AB and SB degrees. It is highly selective, with fewer than five percent of applicants being offered admission in recent years. Harvard College students participate in more than 450 extracurricular organizations and nearly all live on campus—first-year students in or near Harvard Yard, and upperclass students in community-oriented "houses". The college has produced many distinguished alumni, including prominent politicians, scholars, and business leaders.
Title: Harvard–Yale football rivalry
Content:  Decades later the eight universities that administer athletic programs and competition under the auspices of the Council of Ivy Group Presidents, better known as the Ivy League, reiterated reforms rooted in requests made during the series of meetings. Agreements among the athletics departments at Harvard, Yale and Princeton in 1906, 1916 (the "Three Presidents Agreements" on eligibility), and a revision of that agreement in 1923 have been considered precursors to the Ivy Group Agreement, each agreement addressing amateurism and college football. The Ivy Group Agreement, adopted in 1945, states for football, "the players be truly representative of the student body and not comprisedof [sic] a group of special recruited and trained athletes." Harvard president Nathan Pusey and Yale president A. Whitney Griswold collaborated closely toward the eventual implementation of the Ivy League in 1954 with the "Agreement" extended to all sports. Round-robin play started in 1956 for football among programs representing Brown University, Columbia University, Cornell University, Dartmouth College, Harvard University, Princeton University, University of Pennsylvania, and Yale University.

Question: when did harvard become an ivy league school?
Answer: 1945.