In 1838, David Markham was appointed rector of Great Horkesley, near Colchester, Essex. A year later, Clements began his schooling, first at Cheam School, and later at Westminster School. Reportedly an apt pupil, he showed particular interest in geology and astronomy, and from an early age he wrote prolifically, an activity which filled much of his spare time. At Westminster, which he found "a wonderful and delightful place", he developed a particular interest in boating, often acting as coxswain in races on the River Thames.