Complex sentence: He was educated at a secular primary school, after which he went to the three-year HBS high school and from 1897 to 1899 he went to the "Openbare Handelsschool" (a college level business school).
Split into simpler sentences: He was educated at a secular primary school, after which he went to the three-year HBS high school. From 1897 to 1899 he went to the "Openbare Handelsschool" (a college level business school).