The Principals' Federation says schools are becoming much more racially segregated, which is not good for New Zealand society.
An independent study by Pūkeko Research found three quarters of Pākehā children attended decile six to 10 schools in 2013, compared to 61 percent in 1996.
It also found Pākehā now make up just 0.5 percent of decile one students, while Māori make up half of all students in decile one schools.
Principals' Federation president Denise Torrey said the research reflected what they were seeing in schools and had implications for race relations.
"We need to learn tolerance and one of the ways we learn tolerance is by observing others and putting our feet in their shoes.
"If we don't get to mix with those sorts of people, then we don't get to do that."
The Pūkeko Research study also found the percentage of Māori children in decile six to 10 schools has also increased from 21 to 34 percent, but Ms Torrey said that reflected the movement of middle class Māori to middle class schools.
She said giving parents a choice about what schools their children attend had restricted opportunities for those that remain in poverty.
"As lower decile schools get smaller, those that are left in the schools, who are the most needy, have fewer opportunities.
"They are mixing with only their group and don't necessarily see the potential, that there is another way of doing things, setting high expectations.
"When you've got mobility and resources you're able to move, those people who don't have any resources don't have any choices.
"So we're building this racial divide and I don't think that's good for New Zealand society."