Harper joined Cullinane from Waihi College, where he was the deputy principal for four years - he started his career as a maths teacher at Hamilton Boys' High School 20 years ago.
He said that he had always wanted to be a teacher, but becoming a principal presented new challenges and opportunities.
"I don't think you can ever be prepared for being a principal, it's got a wider scope than what you generally think it would be like as a teacher," Harper said.
"As a teacher, you might have 30 students for an hour, you can make a real difference for those individuals, but as a principal you have a greater level of influence for quality education."
Family was a big part of the appeal to move to Whanganui, Justin's wife Nicola Harper is working at St Mary's School, which their three children also attend.
"What a fantastic place to raise children, there are so many opportunities here and the climate's great," Harper said.
"I've had to mow the lawn four times in two weeks, not many places do that in May."
His immediate goals were to get a feel for his new environment, to understand what the hopes and dreams of the students are and to get to know the staff better.
Harper said he hoped his feet would hit the ground in his second week on the job.
"Education is really simple, you take people that are really passionate about what they do and you put young people in the same room as them - that creates inspiration," he said.
"I'm really stoked to be here and it's going to be a fantastic chapter in our family's lives."
