In New Zealand the Charter School policy is aimed at helping the long tail which is predominantly made up of Maori and Pasifika students – more typically in lower socioeconomic situations.
The NY Times has this kind of thing to say about the effects of Charter Schools for this type of group:
Charter schools are controversial. But are they good for education? Rigorous research suggests that the answer is yes for an important, underserved group: low-income, nonwhite students in urban areas. These children tend to do better if enrolled in charter schools instead of traditional public schools.
A consistent pattern has emerged from this research. In urban areas, where students are overwhelmingly low-achieving, poor and nonwhite, charter schools tend to do better than other public schools in improving student achievement.
Charter schools in Boston produced huge gains in test scores. A majority of students at Boston’s charters are African-American and poor. Their score gains are large enough to reduce the black-white score gap in Boston’s middle schools by two-thirds. Boston’s charters also do a better job at preparing students for college.