The student's father, who did not wish to be named, told the Weekend Herald Mr Alexander had said the support was meant to help his son adapt to his new country and make friends at school.
Although international students at the school pay $12,400 plus GST in annual fees, the father said his son was eligible to study as a domestic student because he was in New Zealand on a long-term work visa as a South Korean government employee.
However, he was invoiced $6,106.50 for the services of a language assistant who was used for three hours each day in the last two terms of last year.
The charge-out rate for the service as stated in the invoice was $15 an hour.
Mr Alexander said in his letter that his support was vital to ensure the student "made sufficient progress" to advance into Year 8. However, a Ministry of Education spokeswoman said it was wrong for schools to be charging migrant parents for language support provided during school hours.
"Parents should not be expected to pay these costs," the spokeswoman said.
"It is expected that schools use (ministry) funding and international student fees, if applicable, to provide the support required."
The ministry was not aware of any other schools making similar charges.
The spokeswoman said all schools are expected to provide language support for English language learners, and the ministry's website describes the funding and material resources that schools can access.
Last year, the ministry provided funding for 32,000 students in 1316 schools from an annual budget of $26 million.
"Schools use this additional targeted funding for the provision of specialised [language] support programmes, generally in the form of small group withdrawal programmes," said the ministry spokeswoman.
"It may well be that some parents have been urged to seek and pay for additional English tuition outside school hours for their children."
Mr Alexander said he could not comment on the invoice because of the Privacy Act, but insisted he had followed the rules.
Of the 623 students enrolled at the school last year, 239 were Asian and 26 were fee-paying international students.
"No student is ever excluded from learning support, we are committed to ensuring our students are well prepared for secondary school," Mr Alexander said.
"Excluding the family you refer to, we have not invoiced any family for language assistant services.
"English language support is funded by the ministry and we contribute funds ourselves to ensure that students who need extra support get it," said Mr Alexander in an email to the Weekend Herald.
