Principals in rural North Island towns say poverty and students who leave early are behind the worst NCEA pass rates.
Government figures show school leavers' results are poorest in places like Kawerau, Stratford and South Waikato.
In 2013, 74 percent of school leavers overall had at least NCEA level 2. But in Kawerau the figure was 46 percent, in Stratford 57 percent and in South Waikato and Wairoa about 60 percent. The only other territorial authority with such poor results was Manurewa with 58 percent.
Stratford High School principal Philip Keenan said it is hard to keep students long enough to complete their qualifications and other principals are also battling poverty and isolation.
"We're a farming area and a farming sector at the present time is quite a booming sector. Students can go and get jobs on farms - they might only last on those farms for six months before they make decisions to go to the local tertiary institution or go and do other courses around," Mr Keenan said.
Results are also being dragged down by students bussing out of town to bigger city schools, he said.
However, principals believed that results can be improved by higher expectations, more trades courses, and closer attention to individual students.