Nicholas Eggington was found guilty of two counts of indecent assault and two counts of gross indecency against a male child between 1992 and 1993.
The 58-year-old, who taught at the Cheam School in Hampshire, was placed on the sex offenders' register for life.
He is also subject to a sexual harm prevention order.
Winchester Crown Court heard Eggington, from Nottingham, worked at the school in Headley between 1987 and 1993.
Following sentencing on Friday, a Hampshire Police spokesman said the victim had shown "courage" during the "difficult investigation".
A teacher has been jailed for three years for sexually abusing a boy at a preparatory school.