Three former members of staff at Christ's Hospital in Horsham, West Sussex, were arrested earlier this year, it has been revealed.
The attacks on nine pupils are alleged to have taken place during the late 1980s and early 1990s.
The suspects, aged in their 60s, have been bailed until 15 December.
Two men, aged 65 and 66, were arrested at addresses in Shropshire and North Yorkshire on 29 January respectively.
The 65-year-old was arrested on suspicion of indecent assault on a girl then aged 18 in 1994, indecent assault on a boy then aged 18 in 1990, and indecent assault on a boy then aged 15 or 16, in 1988 or 1989.
The 66-year old was arrested on suspicion of the rape of a girl, then aged 16 to 18, in West Sussex in 1992-94, and indecent assault on a girl then aged 17 in 1994.
A 62-year old west London man was arrested on 12 June, on suspicion of indecent assaults on four girls, then aged between 14 and 17, in West Sussex between 1985 and 1993.
Sussex Police said the men were all members of school staff at the times the offences were allegedly committed.
Allegations of historical sex abuse against pupils at a boarding school, including the rape of a girl, are being investigated by police.