Crown prosecutor Rebecca Guthrie and Judge Cameron were concerned with what they saw as Harter's attempts in interviews to transfer some of the blame to the children.
Defence counsel Tony Snell said Harter often suffered depression. The latest bout was thought to have been triggered by the death of Belinda Harter, who was killed with her partner and nine others in the balloon crash on January 7, 2012.
About 12 members of victims' families dominated the public gallery.
In court, the partly balding Harter, dressed in a dark shirt without tie, stood between two taller prison officers and focused almost unfalteringly on the judge throughout the hearing, which lasted about an hour.
No victim-impact statements were read in court, although Judge Cameron reiterated Crown assertions that the impacts on the children were incalculable and long-term.
In one interview, Harter had admitted he experienced sexual arousal while playing with the children, but he sometimes carried on with lessons afterwards as if nothing had happened.
Detective Lisa Tod said after the sentencing that the families were "devastated" by the offending but were not prepared to comment yesterday.
School Board of Trustees chair Rachel Cornwall said in a written statement the school hoped the conclusion "will assist in helping families to heal and put these events behind them. We appreciate this is a very difficult time for them."
"The entire school community was shocked and saddened by his actions but we are a very united school and we have pulled together even more over the last few months to ensure our school continues to offer a positive learning environment."
She said the board and staff will continue to offer support and assistance to anyone in the school family who needs it.
A teacher with more than 40 years' experience in Masterton, Hutt Valley and Hawke's Bay, Harter is well-known in musical and production circles. He founded a theatre company in Wellington, won awards for theatrical production and appeared in a panel on a television programme helping students solve homework problems.