Demographic changes could see central Auckland schools pull in more students from areas already losing thousands.
Work is under way to check the accuracy of earlier official warnings that declining numbers of students in central Auckland could mean schools looking west and south to fill rolls.
Figures show more than 4280 students already leave West Auckland each day to attend state or state-integrated schools in the old Auckland City boundary.
A principals' council says the resulting inequality is the most important issue New Zealand education faces.
Labour, which received information on the flow of students under the Official Information Act, wants the Ministry of Education to acknowledge the movement as a problem.
Because operational funding is roll-based, if schools cannot fill their roll from within their zone they will often look to attract outsiders.
Demand for secondary schooling will increase in all districts, the analysis notes, except Auckland City which will have fewer students by 2017.
"The large decline in demand for the Auckland City TA [territorial authority] will likely result in secondary schools within this TA trying more so to pull students from West and South Auckland to fill spare capacity."
Carmel Sepuloni, MP for Kelston and Labour's social development spokeswoman, who obtained the information, said it showed officials had been aware of the issue for years.
"But there is no attention paid to it, and there is no strategy that has been put in place ... we have seen results improve [at local schools]. But obviously there is still a perception problem that needs to be addressed."
Katrina Casey, the ministry's head of sector enablement and support, said growth in Auckland had changed significantly in recent years and a report had been commissioned to get a clearer picture.
The ministry said about 60 per cent of secondary students leaving West Auckland attended Avondale College or Lynfield College, schools with zones that border or overlap the territories.
Education Minister Hekia Parata said officials had been asked to focus on factors like quality of teaching, leadership and parental engagement.
"If every school is a great school then most parents wouldn't feel a need to drive their children past their local school to secure a high quality education."
Secondary Principals' Council chairman Allan Vester said the issue was a regular topic of discussion among principals in the west, and there was concern but no sense that it could be turned around.
"Ultimately, the only way to address it is to resource schools in such a way that every school can be a great school that local parents will desire. It is truly the most important issue facing New Zealand education."
Travelling to school
Number of West Auckland-resident secondary school students attending state or state-integrated schools in other parts of Auckland last year:
Intermediate and primary: 1176
North Shore City
Intermediate and primary: 154
Source: Ministry of Education.