Christchurch high school students travel the equivalent of a trip to the moon each week to get to their preferred schools, a study has found.

The students travel 171,984km a day to get to school - 71,487km further than they would if they attended their nearest school.

Fairfax Media has calculated that the students total "unnecessary" travel in a week is 357,435km - almost as far as the 384,000km distance from the Earth to the moon.

Study author Andrew Devonport, a Canterbury University geography student, believes his study is the first of its kind in New Zealand, using Ministry of Education data on the home addresses of all 28,337 secondary school students in Christchurch.

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He calculated that, if every student travelling more than 2km travelled by car, their "unnecessary" extra travel would pump out an extra 156kg of carbon dioxide emissions every day.

However a large part of the "unnecessary" extra travel was due to students attending single-sex schools.

The study does not provide a breakdown of how much travel is to single-sex schools and how much is due to schools' differing decile ratings and reputations. It is hard to separate these issues out because the city's two biggest single-sex schools, Christchurch Boys' High and Christchurch Girls' High, are also high-decile schools with top reputations.

Previous studies have also found large numbers of students travelling long distances to high-decile, often single-sex schools in Auckland. About 3100 secondary students from West Auckland, and 3000 from South Auckland, travelled to schools in the central isthmus in 2014.

Nationally, the Council for Educational Research found that only 50 per cent of parents in Auckland, Hamilton, Wellington, Christchurch and Dunedin said their first choice of secondary school for their children was also their closest school.

Council researcher Dr Cathy Wylie said the single-sex schools tended to draw students from wealthier areas.

"The single-sex schools tend to be longer-established and tend to be the ones offering academic opportunity first, and tend to have a reputation," she said.

"Many of the single-sex schools tend to be higher-decile and quite a few of them are integrated schools, and they tend to have a higher donation level. The cost of attending them tends to be higher than other schools."

Devonport found that school decile rating - the socio-economic status of its students' families - was the only factor that had a significant impact on their market share.

Surprisingly, he found only weak correlations between numbers of out-of-zone students and NCEA pass rates, possibly because most parents did not actually have this data.

He found that Christchurch high school students travelled an average of 6.38km to state schools, 9.34km to integrated (mainly Catholic) schools, and 9.88km to private schools.

But if they all travelled to their nearest schools, they would have to travel only 4.14km.