Following the Austro-Hungarian Empire's advancements in modern secondary education, on 20 November 1854 the first secular gymnasium was opened in Zagreb.

A wide range of new buildings and facilities were constructed and the learning conditions of the school improved drastically.

Also, around this period, writer Franjo Bučar was introducing sports such as football, hockey, gymnastics, and fencing to the nation of Croatia.

During the World War I, the school's building served as a military hospital, the actual institution temporarily re-locating to the site of an orphanage on Vladimir Nazor street.

However, they could not use the full extent of the building for many years afterwards as it was also utilised for housing refugees who escaped Istria after its annexation by the Kingdom of Italy.

Following the establishment of Yugoslavia, sweeping education reforms across the country required all public schools to become co-educational.

[8] Also in 1954, the school celebrated its 100th year anniversary by erecting a plaque with the names of all the students who had died as a result of the World War II.

Ten years later, people left homeless by Zagreb's catastrophic flood in 1964 were housed in the school's buildings while their homes were being repaired.