Gary Dobbie is accused of assaulting the young boy on several occasions while he was a teacher at Christ's Hospital School in West Sussex.
The 67-year-old, who was a head of house at one point and lived in the school grounds, denies three charges of indecent assault between 1986 and 1991.
Now living in Albi, France, after having previously lived in Hereford, he is set to stand trial in April, Sussex Police said.
Prosecutors decided not to proceed with allegations made against him by another of the school's former pupils, a police spokesman said.
Before his arrest, Dobbie was teaching at Shrewsbury School.
Christ's Hospital is one of the oldest boarding schools in the country, dating back to the 16th century when it was founded in London by King Edward VI, who signed a Royal Charter for it just 11 days before his death in 1553.
The Queen is a patron of the site, now based in Horsham and famous alumni include poet Samuel Taylor Coleridge and Sir Barnes Wallis, inventor of the bouncing bomb.