Dr Hattie, a Kiwi and former professor at Auckland University has recently published Politics of Distraction, a "meta study" of his research, based on 60,000 students in several countries.
What makes the big difference in a school, Dr Hattie says, is how good the teacher is - and there are big differences between individual teachers at any particular institution.
These teacher differences are bigger than the differences between schools, according to his research.
Factors with little effect on academic success include class size and teacher aids.
For parents these are groundbreaking conclusions.
They mean that buying a home in a flash suburb with the 'right' school does not increase the chances of your child passing exams.
"How can we have the best teachers - those having the greatest impact - understand better what they do, get them involved, then invite the others to come across and be like those teachers in their impact," is the big question, Dr Hattie says.
That's why I visited a local secondary school -- Green Bay High. Dr Hattie's research indicates the school is fine.
Leah Stewart is a senior teacher in history and social studies, Green Bay was where she had her first teaching job and a teachers college section (work experience.)
For Michael Cole, a senior teacher in science, it is his second school.
I observe Leah's year nine social studies class. The topic is child labour in India.
She uses a whiteboard and laptop connected to a projector, showing a short film of Indian children packing matchboxes in a small town in Tamu Nadu.
Next Leah puts up a telling example -- how much a child has to earn in a day in Indian rupees and Kiwi dollars.
The students type furiously on their laptops and tablets -- not an old-fashioned exercise book in sight.
They break into groups. A crucial exercise is whether they can pack a box of matches in 20 seconds.
Down the corridor at Mike's year 13 biology class the students have already broken into six or seven learning groups.
I sit in some, as he whizzes around.
The topic is evolution.
They use prepared worksheets.
Sometimes he speaks to individuals, sometimes to the group and sometimes to the whole class.
"Evolution is full of extinction events," he says to the class.
"That is a tough question. You are getting into the realm of philosophy of science," he says.
Turns out it's his birthday. A student has baked him a cake -- he notices a picture of DNA on the icing.
"Not hard to Google what DNA looks like," she says.
Dr Hattie talks about a bond between students and teachers.
"First up," says Leah, "You have to like teenagers... We have some amazing students here."
Both Mike and Leah use the technique of "reflection on action" (developed by Brazilian philosopher Paulo Freire and studied at New Zealand universities) to adjust their technique to circumstances.
"Good teachers are always learning. Others don't," Mike says.
They also try to "get bang for their buck."
For example, they recently combined a social studies and a science trip.
They emphasise both subjects are trying to do the same thing: to teach kids skills they will use later in life.
Leah says teaching is inherently isolating so it's crucial to share ideas with other teachers.
One way is the Government's Communities of Schools programme, where nearby primary, intermediate, secondary schools and even polytechnics get together.
The idea is partly to break down the barriers between secondary and primary schools.
Not all of Dr Hattie's findings appeal to teachers.
He has found that lower teacher/student ratios have little effect on students' success -- the opposite of what many teachers say.
Mike says it is impossible to argue with Dr Hattie's rigorous data on class size, so you adjust your technique.
Problem is, Leah says, some teachers do exactly the same thing with 25 students as they did with 32, so it's not surprising that it makes little difference.
