1948
• Tané Matsukata returns to Japan after 17 years in the United States
1949
• Classes begin for four students in the Murata home with three teachers
• Nishimachi School is founded and formalized by the Minato-ku Government
1951
First school building is completed
1953
• First elementary graduation takes place
1955
• Nishimachi School is recognized as Gakko Hojin by the Tokyo Metropolitan Government
1956
• Primary language of instruction becomes English
• Japanese classes begin with two Japanese students
1958
• Kindergarten is added
1962
• Japanese-language studies become a requirement for all students
1963
• Junior high begins with grade seven; grade eight is added in 1964; and grade nine in 1965
1965
• Matsukata House reverts to the Matsukata family from the Venezuelan government
• First edition of Ayumi (school yearbook) is published by grade eight students
• Junior high is relocated to Matsukata House
1966
• School name is changed to Nishimachi International School
• First junior high (grade nine) graduation takes place
• Tradition of annual ski trips begins
• First Food Fair is held
1968
• Student Council (StuCo) is established
1970
• First edition of Nishimachi newspaper CHIHEISEN is published by grade seven and eight students
• Camp Rioichiro Arai is dedicated at Kazuno, Gunma-ken
1973
• First Japanese program and speech contest are held
1975
• 25th anniversary is celebrated CHIHEISEN article
1979
• Alumni group holds surprise 30th anniversary party for Miss Matsukata (read secret invitation)
1980
• Tomo no Kai (parent association) is formed
• First issue of The Internationalist is published
1984
• 35th anniversary is celebrated (CHIHEISEN article)
• CHIHEISEN celebrates 100th edition
1985
• Phase I building (Ushiba Memorial Gymnasium) is completed
1986
• Nishimachi is accredited by WASC (Western Association of Schools and Colleges)
• Phase II building (primary building) is completed
1989
• Founder, Tané Matsukata, passes away
• Tané Matsukata Fund for International Education (scholarship fund) is established
• 40th anniversary is celebrated in honour of Tané Matsukata (The Internationalist article)
1990
• New lodge at Camp Rioichiro Arai is completed
1991
• Nishimachi-Kai (alumni association) is formed
1993
• Japanese presentation program replaces Japanese speech contest
1994
• Sister school ties with Kurohone elementary and junior high school are formalized
1997
• Phase III building (upper elementary and junior high building) is inaugurated
1999
• WASC (Western Association of Schools and Colleges) self-study is completed and six-year accreditation awarded
• 50th anniversary celebrations are held over three days (The Internationalist article)
2000
• Middle school program replaces junior high school
2001
• ERB standardized testing begins
• Nishimachi builds and supports Kirivorn School in Cambodia
2002
• Kindergarten is relocated to the Moto Azabu Hills complex
2003
• Outreach Scholarship Program for Student Diversity is established
2004
• Tokutei Koeki Zoshin Hojin (Special Public Interest Promotion Organization) status is granted by Tokyo Metropolitan Government
2006
• WASC (Western Association of School and Colleges) and CIS (Council of International Schools) ten-year joint accreditation is awarded
2007
• Phase IV building (Yashiro Media Center) is inaugurated
• Multi-purpose area, under the gym, is renovated
2009
• Reinforcement work of the Matsukata House is completed
• Enhanced art program of music, performing arts, visual arts, is implemented for both middle school and elementary school
2011
• The Great East Japan Earthquake hits Tohoku area Nishimachi relief projects are conducted
• Renovation of Farm House at Camp Rioichiro Arai is completed
2015
• 65th anniversary is celebrated
2016
• CIS (Council of International Schools) and WASC (Western Association of School and Colleges) ten-year joint accreditation is awarded