A second student at Mt Albert Grammar has been confirmed as having had Covid-19.
The student was infectious more than two weeks ago, the school said in a newsletter to parents and caregivers.
Other students or staff may have caught the virus from August 5 to 11.
All students and staff are now being asked to get tested if they have not been tested since August 17.
"The student was at school in the week before lockdown," the newsletter said.
"There is a possibility that other students or staff may have caught the virus from August 5 to 11."
Auckland Regional Public Health Service (ARPHS) is asking all students and staff members to get tested if they have not been tested since August 17.
"This will help identify if there are any undiagnosed cases. No further cases have been found at the school so far, except for these two known cases. We would have expected to have seen other cases by now if there was widespread transmission."
The first case of covid at the school was on August 12 when a pupil turnturned up to classes on the Monday before a region wide lockdown, unaware he was infected.
The teenager was later linked to a family who were one of the first identified in the Auckland cluster, which has now become the largest in New Zealand.
There are now 108 people infected in the cluster.
At the time about 100 pupils and a handful of staff were put into self-isolation for a fortnight, with no sign that anyone else at the school had contracted the contagious virus.