1903 – Tallinn Elementary School No 2 is founded at 6A Poska Street.
1917 – The school is renamed Tallinn Elementary School No 21.
1923-24 – A new schoolhouse is erected at 6 Raua Street. Architect: Artur Perna.
1940 – On 21st June the soldiers of the Signal Battalion of the Estonian Defence Army based in the schoolhouse resist the siege by the invading Soviet Army.
1945-46 – Secondary school level courses of study are introduced.
1950 – First 14 students finish secondary school.
1958 – The first specialised music class opens.
1961 – The first art and English specialised classes start. The first annual school concert is held in the Estonia Concert Hall.
1965 – An annex building for primary students is completed. Architect: Heili Härmson.
1966 – The first educational institution in the Soviet Union to introduce a shorter five-day week.
1967 – Construction of the new swimming pool and gym is completed.
1986 – The first Week of Art and Culture is held.
1987 – The school gets its flag and a graduation ring, designed by Andres Ojari.
1988 – The first student exchange programmes are conducted with the Dalton School, New York, Kingswood Oxford School, CT and Mariner High School, WA, USA.
1991 – The first issue of the school newspaper ’Lennuk’ (’Airplane’) is published.
1993 – The school joins an international initiative for promoting healthy lifestyles in schools.
1994 – The exchange programme with Lahti school in Finland starts.
1995 – The School Student Council is established.
1996 – A joint co-operative body of Five Schools (G5) is initiated by Tallinn Secondary School No 21.
1996 – The school joins The Baltic Sea project.
1997 – The first computer classroom is equipped. Following the students’ initiative National Defence courses start.
1998 – The school is renamed Tallinn School No 21.
1999 – The school gets its school cap. Designer: Jan Garšnek, alumnus ’50.
2000 – The school is awarded the title of ‘A European of the Year’.
2001 – Renovation of the school building starts. Lessons are temporarily transferred to other schools.
2002 – A three-school project of humanities commences. The participants are from Hugo Treffner Gymnasium, Pärnu Sütevaka Gymnasium of Humanities and Tallinn School No 21.
2003 – The school celebrates its centenary with the opening of a newly renovated building designed by architects Raul Järg and Toomas Korb.
2003 – A book about the history of the school ‘A Hundred Years of the School Bell’ is published.
2005 – The school is awarded a certificate for outstanding extracurricular activities.
2006 – Transition to the online system ‘e-school’ is completed.
2007 – The tradition of staging musicals in cooperation with German students from partner schools is established, ‘Hans and Grethel’ being the first production.
2009 – Student initiative leads to the introduction of school waistcoats as an element of uniform.
2010 – The 50th annual school concert is held.
2011 – The 25th anniversary of the Week of Art and Culture is celebrated.
2012 – The school is awarded a certificate for outstanding learning environment.
2013 – Tallinn School No 21 celebrates its 110th birthday.
2013 – A film introducing the school is released.
2014 – The school is presented a certificate for ‘Innovative Act 2014’.
2015 – The school is presented a certificate for ‘Innovative Act 2015’.
2016 – The school is recognised as an ‘Innovative Learning Establishment 2016’.
2016 – The is awarded ‘Best Cooperative Project 2016’.
2017 – The school is recognised by the city of Tallinn as School of the Year 2016.
2017 – The school is awarded a certificate for its digital activities by the Ministry of Education and Research.
2017 – The school is awarded a certificate by Education in Tallinn for ‘Education Act’ and a special prize for participation in the Flower Festival.
2018 – The school is awarded a certificate by Tallinn Education Department for “Education Act 2018” in recognition of opening the innovation studio EduInnoLab.
2018 – The school receives recognition from Tallinn Education Department as “Enterprising school 2018”.
2018 – The school receives Tallinn Education Department’s recognition and award for “Education Innovation 2018”.
2018 – The School receives Tallinn Education Department’s recognition and award for the “Best Cooperation Project 2018” .
2018 – The school gains national and international recognition for receiving the 2018 Quality Innovation Award.
2019 – On the 27th of February 2019, the winners of the annual Quality Innovation Award competition were announced in Beijing. Tallinn 21st School received the award for Education sector innovations for its Specialised classes in Entrepreneurship and Robotics.