Complex sentence: St Joseph's was closed between 1941 and 1946 because of the war, but by the late 1950's enrollments had risen and the school's facilities had become too small to cater for the children's needs.
Split into simpler sentences: St Joseph's was closed between 1941 and 1946 because of the war. Enrollments rose steadily after the war and by the late 1950's the school's facilities had become too small to cater for the children's needs.