He confirmed that a laptop used by the then principal Jill Lees had been stolen and reported to police at the time.
He said he believed the theft was not linked to the tampering of data and the theft had not been a hinderance in the investigation on data tampering.
Ms Lees has since resigned from her role at the school. Mr Grindle said she had left for "personal reasons" and the board was looking at appointing a relieving principal before the position was advertised.
He said steps have been taken to strengthen procedures involving school data.
"We've since strengthened the procedure around the use of passwords," Mr Grindle said.
"The matter has been resolved, it's concluded. It happened in November last year and eight months down the track we're moving forward."
Parents and the ministry have been informed of the investigation's outcome, said Mr Grindle.
The ministry's head of sector enablement and support, Katrina Casey, is confident of the steps taken by the board of trustees.
"The school has introduced changes to prevent this happening again.
"We are satisfied with the steps the school has taken."
The Board of Trustees released a statement saying that in December 2013 they were informed the National Standards had been tampered with and launched an investigation.
Data tampering of this nature had not occurred previously at the school.
New Zealand Educational Institute Te Riu Roa president Judith Nowotarski had said while the actions of an unidentified staff member at the school could not be condoned, overseas experience showed these types of incidents were a sad but almost inevitable outcome of bad policy such as National Standards.
Ms Nowotarski said this case should ring alarm bells for the Government.
"We don't need 5-year-olds labelled as failures. We don't need schools ignoring the wider curriculum to focus solely on the three Rs of National Standards."
She said New Zealand didn't need staff so stressed and fearful that they changed results.
Education Minister Hekia Parata would not comment, saying it was an operational issue.