Education
He attended the Frederikshald Gymnasium and graduated with the examen artium university entrance exam in 1891. He subsequently studied philosophy and natural sciences at the Royal Frederick University.
He attended the Frederikshald Gymnasium and graduated with the examen artium university entrance exam in 1891. He subsequently studied philosophy and natural sciences at the Royal Frederick University.
He is also known for the widely used Haffner og Haagaas series of textbooks in mathematics, which was published between 1925 and 1979 in numerous editions. He also served in the Royal Norwegian Navy 1897–1902 as a deputy intendant (second lieutenant in the logistics officer corps). He was employed as a lecturer in mathematics at the private gymnasium Frogner School in Oslo in 1900, and was a co-owner of both Frogner School and its neighbour, the Nissen"s Girls" School, from 1913 to 1918.
Haagaas School was the last school in Norway in the tradition of the Heltberg School of the 19th century, offering a fast track to the examen artium (a so-called studentfabrikk, "student factory"), and was described by Mosse Jørgensen as "the new Heltberg." He was a co-author and subsequently the sole author of the Haffner og Haagaas series of textbooks in mathematics, which was published between 1925 and 1979 in numerous editions.
According to Aftenposten, he was one of the most well known Norwegian educators at the time of his death. He grew up in Tistedalen outside Frederikshald, the son of Theodor Christian Haagaas (1823–1899), managing director (1862–1892) of the sawmills of Saugbrugsforeningen, Norway"s largest timber company, and Nora Martha Petersen (1845–1887), who was born in Norway to Swedish-born parents.
Theodor Haagaas was one of the pioneers of skiing in Tistedalen around 1885–1886. They had four daughters, among them the humanist Henriette Bie Lorentzen.
Theodor Haagaas was the maternal grandfather of Labour and Welfare Director Joakim Theodor Haagaas Lystad.