According to written evidances, by 1900’s the academic staff had consisted of a principal and seven teachers. Moreover during this period school has been uplifted as a bilingual school and they have introduced evening classes to teach Tamil and Arabic languages. These two changes have attracted the attention of other nationalities and religion followers. By 1925, Theldeniya National School has been acknowledged as a regional sport conference centre for all other schools in the area.
After 1963, a dawn of a golden era of the school has been marked as Edmand Wijesinghe took over as the princial position. He was an aesthetic person who has acted as the “wadi” king in Ediriweera Sarathchandra’s “Maname”. During his era, Sports and drama sections of the school have been developed greatly. He has introduced the tradition of holding a drama festivals at the end of each year, which continues even today. School song has also been introduced in the era.
In 1974 A/L science section has been established in part to the introduction of the eastern band. As per the evidences, the school has grandly celebrated 25th anniversary in 1979. In 1983, Theldeniya National School has been victimized by the flooding of the Victoria Reservoir constructed by the Accelerated Mahaweli Project.Consequently the school has been shifted to newly build buildings.
In 1992 the school has received high popularity as a result of the presidential mobile service project. This has resulted in physical and human awakening which include repairing of all the building constructions of a safely fence around the school, placing a magnificent name board and getting water and electricity facilities.