"I'm really proud to have helped pull together a very good team and that's one of the reasons I can make this move, because the team is so strong."
The senior leadership, middle managers and heads of faculties were "very solid" and quality teachers had helped seal his decision to step down, Mr Hullena said.
Deputy principal Kellas Bennett would be an "ideal" successor, he said, should he choose to make a bid for the role.
"It's a hard move for me but the right move, and it's a perfect opportunity for the school to get some new energy and perhaps new ideology, to keep the momentum going.
"One of the things that helped us that is different to traditional schools, that helped us grow, has been the strength of our relationships. Student to teacher, senior leaders to staff, staff to community and principal to board; our whole philosophy was built around strong relationships.
"What's been behind the long hours is having a job that's got a noble mission. It inspires me and drives me because the outcome is so important."
Mr Hullena is a Wairarapa College old boy who first taught in 1981 before working for a time as a truck driver, a freezing worker, and a New Zealand Army soldier.
He returned to the classroom "like I've always done" and after a break next year may return to the education sector "because it's all I know now" or to further his own studies.
"I've really enjoyed the Makoura community, particularly the parents," he said.
"I've taught in six secondary schools and our Makoura parents have been the most open and willing to work. The willingness of our whanau to work with the school has been enlightening, and a privilege."
Other agencies and groups he praised "for offering support after seeing the need here at Makoura" include Lands Trust Masterton, Trust House, UCOL Wairarapa, and Wairarapa REAP.
"What's making it really difficult to leave is the fact that we're finally seeing collaboration in Masterton between key agencies.
"There are unified approaches in place so no child is left behind, no matter what school they're leaving from.
"It's more about being collaborative and not competitive and that whole concept of having an education plan for Masterton is a great idea; every school working toward that one plan. Schools should be serving their communities and it's an exciting era we're moving into that augurs well for our town."
Makoura College Board of Trustees chairwoman Sara Feringa said Mr Hullena would be greatly missed and the board "looked forward to a new phase" that would build on the successes he had helped achieve.