The money came out of the school's annual operational grant from the Ministry of Education.
Colleen Gray used Mayfield Primary School funds to pay for trips to Australia for her and Bruce and other purchases including food, flowers and Koru Club parking.
Fake invoices were filed so payments were made to companies owned by Bruce Gray.
Some of this appears to have been used for the pair's trip to London for "teacher recruitment purposes".
Phillip Logo was chairman of the school's board of trustees from 2005 to early 2007.
He said the board had an inkling something was wrong, but Colleen Gray controlled what financial information it was shown.
She also created a climate of fear among teachers, making them afraid of speaking out, Mr Logo said.
He gave evidence at the trial this week and said he was more than happy to take time off work to help secure a conviction.
"Thirty thousand dollars is a lot of money at a school that doesn't have many funds. It meant resources that could have gone to kids and for teachers didn't go where it was supposed to."
Wayne MacGillivray took over as Mayfield's principal in early 2011.
The school had moved on positively since Colleen Gray's time there and now sported a new logo, mission statement and bullish attitude.
"Our focus is around student achievement," Mr MacGillivray said.
"There's a really good story to tell there because our kids are progressing well. They are achieving above the kids in comparable schools," he said.
He would like to see the Grays pay reparation to the school, which he said would be spent on digital technology.
Bruce Gray declined to talk when contacted at the pair's central Auckland apartment after their court appearance yesterday.
They have previously proclaimed their innocence in the media.
"We are completely innocent. We have nothing to hide. We will fight these charges," Colleen Gray told the Herald on Sunday in 2012.
The Grays were bailed until sentencing in May.
Colleen Gray faces a maximum sentence of 10 years' jail and Bruce seven years'.
What they've admitted
• Colleen Gray: Nine charges of dishonestly using a document and two of using a forged document.
• Bruce Gray: Four charges of dishonestly using a document.