The schools surveyed had a total of 7352 students. Of those, 1092 students needed extra food when they came to school, he said.
Taking into account there were 105 more schools in Northland that did not respond, the total number of students was likely much higher.
"Even if it's 1000 kids it's disgusting," he said. "I was quite astounded."
While some of these students would be fed by organisations like KidsCan, in many cases schools were feeding them out of their own pocket, Mr Newman said.
The feedback he had from principals since the survey was the crisis was not lessening and they were not being listened to.
"Above all was the extreme anger that was being voiced when Mr Key said what he said. It was like [the Government] were saying. 'We don't believe you'." Last month, a bill called Feed the Kids, that sought to feed one and two decile schools, was voted down by National, Act and United Future parties.
In Parliament, Mr Key said he did not believe the issue was as widespread as Green MP Metiria Turei, who sponsored the bill, was purporting it to be.
"I think there will be some children who go to school without lunch, but I think that number is actually relatively small," Mr Key said.
A spokesman told the Northern Advocate Mr Key stood by the statement, despite the results of the Northland survey.
"As the Prime Minister has said, his statements were based on a range of sources including visits to schools and discussions with principals," the spokesman said.
Following the election, Mr Key said tackling child poverty was one of his top priorities. Asked when an announcement on the issue would be made, the spokesman said work was underway and "an announcement will be made in due course".
"This Government has repeatedly said that the best route out of poverty is through work and New Zealanders are benefiting from our growing economy through more jobs - with 80,000 more people finding employment in the past year - as well as rising incomes and more effective support for families."