Up to a third of students at some schools are getting someone else to read and write their exams for them - but students needing help at many poorer schools are missing out.

Huge gaps between deciles and individual schools in special assessment conditions for the National Certificate of Educational Achievement (NCEA) are raising questions about whether the system is fair.

"It's clear that there are some inequities in students not being able to access these special assessment conditions," said Secondary Principals Council chairman James Morris.

The data, provided by the NZ Qualifications Authority under the Official Information Act, shows