The school was situated in the building of the Tartu Secondary School No. 1. In 1944, the Soviet Union once again opened the Tartu Secondary School No. 1 in the original building, led by director Karl Maasik. Since the school was merged with Tartu Secondary School No. 1, the founding of the school was considered to be the year 1880. From 1950 to 1953, the director was Juhan Truus, from 1953–1956 the position was held by Elmar Loodus. The Russification and Stalinism era from 1944 to 1954 was not well received by the student body. Underground resistance groups such as "Blue-Black-White" (Sini-Must-Valge), named after the colours of the banned Estonian flag, were formed amongst the student body. Extracurricular activity, however, was quite active during that period. Popular were sport, music (including a jazz-orchestra), acting, art and natural sciences. In 1954, the all-boys school became a mixed-sex establishment. In 1958, the official name of the school became A. H. Tammsaare's Tartu Secondary School No. 1. The position of school director was held by Allan Liim from 1956 to 1970, by Uno Langer from 1970 to 1975, by Laine Raudsepp from 1975 to 1987. During the period of Khrushchev Thaw, the Tartu Secondary School No. 1 opened the first special class in mathematics in 1961. In 1964, a special class in physics was also opened. In 1969, the two were merged and the school gained a science-focused department. In 1976, the elementary school moved into a new building, the so-called "little house" ("väike maja"). From 1954 to 1990, the extracurricular activities were focused on school subjects. The literature club published the paper "Our School" ("Meie kool") and eight publications of the almanac Sulesepad ("Pen smiths") were released from 1960 to 1974, with the 9th volume released in 1989. From 1987 to 2001, the school director was Helmar Jõgi. With the Soviet Union nearing collapse in 1990, the school was once again officially named Hugo Treffner Gymnasium. The newly restored establishment was organised into a 6-class primary school and a gymnasium with a progymnasium. In 1995, the primary school and the progymnasium were merged into a separate school and Hugo Treffner Gymnasium stopped accepting students to the 7th form. Since 1998, the school has been a gymnasium consisting only of forms 10 to 12, with the primary goal of preparing students for university. In 1998, the school's southwest wing was greatly damaged in