John Sidney Denham, 67, was sentenced to 19 years and 10 months after pleading guilty to a range of charges, including multiple counts of indecent assault against boys aged five to 16.
Denham was found guilty of abusing 39 boys at schools in Sydney and elsewhere in New South Wales between 1968 and 1986.
"The indecent assaults involved multiple children, often significant planning, were frequently sadistic and overall persistent, objectively serious, criminal courses of conduct," Judge Syme said, according to Australian news agency AAP.
"The offender's actions contributed to a culture of fear and depravity, especially at the school, which allowed these disturbing offences to occur and then remain unpunished for years."