Choosing the best school for your child is an important decision. The best school, whether it is primary or secondary, can have a big impact on your child’s wellbeing and success in school. At least, that is what we currently believe. So far there has been no evidence to prove this or otherwise.

For most parents this decision comes down to where they live, local word of mouth and what they’ve inferred from a school’s decile ranking. In many cases, parents use decile as a proxy for school quality, where the general attitude is, the higher the decile, the higher the quality.

For some parents the decision on where to live is – in part – determined by what schools are available within a zone. Real estate agencies have acknowledged this and often include school zones and the decile rankings of nearby schools when listing new homes on the market.

However, the decile system was not designed to indicate the quality of a school. It was designed for school funding to help reduce barriers to learning faced by children from lower socioeconomic communities.

The problem arises when schools of different deciles are compared using average NCEA pass rates. School compositions can vary significantly, both across deciles and within the same decile.

Students from the lowest decile schools have on average, parents with less income and less education than students from the highest decile schools.

The comparison of schools with students from different socioeconomic backgrounds is unfair.

So how do you know which school to send your children to? Is decile a good proxy for school quality? Reports from the Education Review Office (ERO) can be helpful, but you almost need specialised training to understand how different schools are performing.

The New Zealand Initiative’s solution is utilising the vast amounts of microdata in the Integrated Data Infrastructure (IDI). The IDI is New Zealand’s largest research database, containing data from a wide range of government agencies, including the Ministries of Education (MoE), Health (MoH), and Social Development (MSD).

By merging education data with socioeconomic background data available in the IDI, we will be able to estimate the value a school adds to its students controlling for every student’s socioeconomic background.

We expect that NCEA league tables overstate the differences across schools, because they do not adjust for the differences in the students each school teaches. But the data will tell us, and you, how big the differences in outcomes across schools really are.