Retirement savings, lavish family holidays or private dance lessons: these are some of what the cost of a private education in New Zealand could buy according to the New Zealand Herald's calculations.

The paper ran a story last Sunday questioning why New Zealand parents choose private schools for their kids. Many justify the choice based on personal sentiments about the social aspects, better facilities and unique character of the schools. Still, others invested in the schools because they encourage competition inside and outside the classroom. Presumably similar reasoning applies to those keen to invest thousands of dollars in real estate so that their children can attend higher decile schools.

For those who value academic excellence there lacks systematic and objective ways to determine whether these schools are in fact doing the best they can for their students.

Higher decile schools and private schools consistently occupy the top spots on school league tables. Decile rating has become synonymous with quality, as has the comparison between private and public schooling. But it is not possible to determine from raw school comparisons which school has added the most academic value to the students it teaches.

There is no hard evidence that those who attend these schools wind up achieving more than they would have if they were in lower decile schools.

There exist opportunities that can act as a valuable lens to evaluate school effectiveness but many are yet to be exploited. The InZone programme is one example.

The programme provides boarding facilities for students from lower decile areas who could otherwise not afford to live in Auckland Grammar and Epsom Girls Grammar school zones.

A test of the programme’s success and of the effectiveness of these ‘better’ schools would be to compare the achievement of the students who applied and were selected into the programme with that of the students who applied but were not successful and remained in lower decile schools.

Telling signs would be if the InZone students improved academically compared to prior achievements, as well as performed better than those students not selected. InZone has five years’ worth of data with great potential to contribute to school improvement discussions.

Unfortunately the cost of choice for those who value academic excellence currently rests on incomplete information. New Zealand needs to get better at identifying relative school strengths. After all, it is all about trade-offs.