In the New Zealand education system, decile was a key measure of socioeconomic status used to target funding and support schools. In academic contexts the full term "socioeconomic decile" or "socioeconomic decile band" was used.

A school's decile indicated the extent to which the school draws its students from low socioeconomic communities. Decile 1 schools were the 10% of schools with the highest proportion of students from low socio-economic communities.

This system was implemented in 1995 and later replaced by the Equity Index in January 2023.

A school's socioeconomic decile was recalculated by the Ministry of Education every five years, using data collected after each Census of Population and Dwellings. They were calculated between censuses for new schools and merged schools, and other schools may move up or down one decile with school openings, mergers and closures to ensure each decile contains 10 percent of all schools. Current deciles were calculated in 2014 following the 2013 census (delayed two years due to the 2011 Christchurch earthquake). The previous deciles came into force in 2008 following the 2006 census.

Before the deciles were calculated, Statistics New Zealand calculated the following factors in each individual meshblock (the smallest census unit, consisting of about 50 households each), disregarding any household in the meshblock that did not have school-aged children:

Each school provided a list of the addresses of its students to determine which meshblocks are used. For each of the five factors, the average for the school is found by adding together the factor in each of the applicable meshblocks, adjusting for the number of students at the school living in each meshblock. All schools in New Zealand were then listed in order for each factor, and given a percentile for that factor. The percentiles for each factor are then added together to give a score out of 500. When the score is ordered, the list of schools was divided into ten, giving one of the ten deciles.

This gave a broad measure of the relative poverty, or aggregated socioeconomic (or social class), of the parents or care-givers of students at the school, with decile 1 schools being the 10% of schools with the lowest socioeconomic communities and decile 10 schools being at the other end of the scale.

Note that some types of schools acquire a decile rating regardless of the socioeconomic status of the school community. For example, teen-parent units always "belong" in decile 1, because of the inherent effect teenage pregnancy and parenthood has on teen parents' socioeconomic status, regardless whether the teen-parent unit is in a high SES area or attached to a high-decile school.