Kenneth Francis, 72, assaulted the boys while he was teaching at Widford Lodge Boarding School in Chelmsford in the 1970s.
On some occasions he gave alcohol to the victims – who were all under 16 – before assaulting them.
He was found guilty of 15 counts of indecent assault and two counts of indecency with a child after a two week trial at Chelmsford Crown Court.
The offences came to light in April 2017 when one of the victims reported that Francis had sexually assaulted him. Then, when Essex Police investigated, further allegations were uncovered.
Francis was bailed and will be sentenced next month
If you, or a loved one, have been affected by sexual abuse, please do not hesitate to contact our team of experienced lawyers who will be happy to speak to you about whether it may be possible to bring an abuse claim..