 In 1924 he received his Ph.D. in Leiden under supervision of J. C. Kluyver.From 1926 to 1928 he studied at the universities of Göttingen and Hamburg, and he was assistant at the University of Münster from 1928-1930.Kloosterman was appointed "lector" (associate professorship) at Leiden University in 1930 and full professor in 1947.