Treasury documents reveal officials have doubts about the Government's plan to introduce charter schools.
The Government wants to introduce privately-run, publicly-funded charter schools, also known as partnership schools, in 2014.
The documents say charter schools could be used to test new methods for improving student achievement.
However they also show Treasury is not convinced the benefits of introducing the schools will outweigh the costs and risks.
The papers express scepticism that increasing competition between schools will improve the education system.
The documents show both the Treasury and Ministry of Education opposed the Government's plan to allow partnership schools to hire unregistered teachers.
Treasury told the Government that teacher registration is an indication of a minimum level of quality.
The primary teachers' union says official documents show the Government ignored its advisors when it decided to let charter schools use unqualified teachers.
The Government plans to introduce charter schools, or partnership schools as they will be known, in 2014.