The Ministry of Education must improve the way it helps failing schools, the New Zealand Initiative says.
The think tank has published a report, Signal Loss: What We Know About School Performance, that calls for an overhaul of how school results are measured and reported.
The report said the school system was generally doing well, but there was persistent poor performance.
It said current measures of school performance focused on achievement rates in the NCEA and National Standards in reading, writing and maths, which did not take account of students' starting points and therefore masked the effectiveness of their schools.
The report's author, Martine Udahemuka, said 8 percent of schools had failed Education Review Office reviews and a third of those had done so for at least two consecutive reviews.
She said government agencies should be using information about what worked and what did not to improve schools.
"What we found concerning is that the amount of data and information that's available on the interventions that have happened over these many years in schools are not being used to systematically find out what works and what doesn't work in which challenges."
Ms Udahemuka said most of the schools that failed to improve were small, rural schools.
Ministry of Education deputy secretary of early learning and student achievement Lisa Rodgers said it reviewed every intervention and was changing the way it helped failing schools.
The government was working on multiple initiatives to address challenges such as poor performance, she said.
Those included the Investing in Educational Success programme, which groups schools together, and setting targets for early childhood education participation, NCEA achievement, and the numbers of 25- to 34-year-olds with a Level 4 qualification.