David Hope, 74, assaulted the pupil at the independent Malsis School in Cross Hills, North Yorkshire, in the 1980s.
Bradford Crown Court heard Hope had preyed upon the boy and exploited him due to his age.
Hope was found guilty in December of three serious sexual assaults, three charges of indecent assault and one of indecency with a child.
The boy's parents sent him to the preparatory school near Skipton in the hope he would receive a first-class education, develop his character and improve his life chances, the court heard.
Instead, his experiences had scarred him for life and continued to greatly affect him, the victim said in a statement.
Judge Ahmed Nadim, sentencing, said the former pupil had been forced to relive his "horrific experience" during Hope's trial.
The judge said Hope had robbed the boy of his childhood and undermined his life's potential, and "inflicted severe psychological harm" upon him.
He told Hope, who appeared in court via video link, that he had a "deep-rooted" perversion and sexual interest in young boys.
After hearing that the defendant had been jailed in the 1990s for offences against other boys, the judge added an extra year's licence to Hope's 17-year custodial sentence, remarking that he was "an offender of particular concern".
He also ordered Hope, of Granby Close, Headingley, Leeds, to be placed on the sex offenders register for life.
Nicholas Worsley, defending, said his client was "frail and infirm" due to his age, and there was "a real risk he will he will live out the remainder of his days in custody".
