Peter Webb, 74, pleaded guilty to 11 charges related to child abuse at Christ's Hospital School, in Horsham, West Sussex, between 1974 and 1984.
The youngest of his victims was 11-years-old. A single charge has been left on file.
Webb, who now lives in France, will be sentenced on 12 October.
Three other men, who also taught at the school, are facing similar charges.
Gary Dobbie, 66, who lives in France, pleaded not guilty to 11 charges relating to two boys and two girls between 1990 and 1999.
James Andrew Husband, 67, from York pleaded not guilty to 9 charges of indecent assault and rape against one girl between 1990 and 1993.
Both men will stand trial on 29 May 2018 listed for at minimum 3 weeks.
Ajaz Karim, 62, from London, who is head of squash at Eton College, pleaded not guilty to 9 indecent assaults and 1 attempted indecent assault on six females between 1985 and 1993. His trial was set for 3 April 2018 expected to last 5 to 7 days.
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