Usage of the Reading Recovery programme by pupils from poor homes is not high.
Ministry of Education figures show only 55% of Decile One schools use Reading Recovery.
In contrast, the take-up was 68% in Decile 10 and 74% in Decile Nine schools.
Radio New Zealand's education correspondent says underachievement is marked in low decile schools.
Reading Recovery is not offered in some schools with high numbers of Maori students.
Although Maori students figure disproportionately in negative education statistics, the figures show 70% of Maori six year olds were in schools where the programme is offered.
Reading Recovery was developed in New Zealand in the 1970s by the late Dame Marie Clay.
It is used to help children who are falling behind in reading and writing after a year at school and is regarded as one of the three best literacy programmes in the world.
Last year, almost 11,000 children - 14% of the country's six year olds - were in Reading Recovery.
The Ministry of Education says it all schools are encouraged to use Reading Recovery.
But policy and schooling group manager Kim Shannon says it's up to the schools which literacy programmes they use.
Principals Federation president Ernie Buutveld says the cost is putting schools off.
A team from York University in England and John Hopkins University in the United States recently reviewed 96 evaluations of reading programmes.
Reading Recovery was found one of the world's best for struggling readers, with strong evidence of effectiveness.