Trevor Bolton, 77, from Clacton-on-Sea in Essex, is accused of abusing eight boys over a 20 year period at Carmel College in Wallingford, Oxfordshire.
He denies 16 counts of indecent assault, six counts of indecency with a child, and three other sexual offences.
One of the alleged victims said Carmel was regarded as the world's "premier" Jewish school.
Mr Bolton is accused of carrying out the abuse against boys aged 11 to 15 between 1968 and 1988.
One of the alleged victims told a jury at Oxford Crown Court he felt like a "fish out of water" arriving at the school.
He said: "There was more wealth than I had ever seen."
The court heard Mr Bolton lived on site and told the then-pupil he could visit his home whenever he felt homesick.
He said this was when a "routine" of sexual abuse started that lasted for roughly three years.
"I can't remember when it went from being cuddled to being naked. But it became every night or almost every night.
"There is a point in time when you feel what is going on but you feel trapped."
He said he felt "special" as he had access to Mr Bolton's flat but said he was also "desperately unhappy".
Carmel College was housed at Mongewell Manor House from 1948, but closed in 1997.
Mr Bolton denies all the charges.
The trial continues.
An alleged victim of sexual abuse by a former teacher at a prestigious Jewish boarding school said he felt "trapped".