He was the head of a department at the time of his arrest.
Principal Peter Gall told the Weekend Herald Gillard had been dismissed this year.
Mr Gall said he had "expected more" jail time to be imposed at yesterday's sentencing, but he was happy with the outcome.
"He's certainly where he deserves to be.
"I echo the comments that the judge made regarding the courage needed by the people who were victims.
"They went through the court process which must have been a difficult thing for them to do.
"I take my hat off to them and congratulate them. Certainly if they hadn't done that, he might still be out there offending today."
Mr Gall said the sentencing brought closure for the victims and meant the school could move on from Gillard's offending.
Alongside the sex charges, Gillard was sentenced on a charge of attempting to flee the country to avoid trial.
After his arrest, Gillard was required to surrender his passport to police as a condition of bail.
He then applied for a new passport, filling out travel documents in the name of his brother-in-law.
He allegedly supplied photographs of himself.
Police were alerted when "irregularities" in the application were discovered - most likely by facial recognition technology used by the Department of Internal Affairs to identify false passports.
Counties Manukau police began investigating Gillard after they were approached by the grandmother of one of the victims.
Text messages between the pair were discovered by police.
Gillard's sentence
• 4 years' imprisonment for four charges of sexual connection with a young person.
• 3 years 5 months' imprisonment for six charges of indecency with a girl between 12 and 16 and one charge of encouraging commercial sexual services.
• 18 months' imprisonment for three charges of supplying methamphetamine.
• 6 months' imprisonment for one charge of breaching the passport Act.
• Total - acumulative sentence of 9 years and 5 months.