The school will be closed tomorrow and Tuesday as staff, students and the wider school community deal with the news.
In a letter to parents today, board of trustees presiding member Ronda Tokona said with "incredible sadness" she was informing parents that Ms Mouat died at home, peacefully on Saturday.
Ms Mouat was remembered as a "warm, vibrant, nurturing, invaluable educator, and an inclusive leader".
"We extend our heartfelt condolences to Kristan’s family during this painful time.
"Our thoughts are also with the entire staff of our kura, many of whom had the privilege to work and grow alongside Kristan for many years."
She said the board was committed to supporting her co-principal Peter Hills and the school’s leadership team.
The board had closed the school for two days as the school community dealt with the "devastating news", she said.
The news was posted on the school’s Facebook page today as well and Ms Mouat received many tributes.
"What a huge and irreplaceable loss," one wrote. "Ms Mouat was not just an amazing educator but a beautiful soul who deeply cared about all of her students. Sending so much love and light to her whānau, friends and the entire school community who will all be deeply affected by this tragedy."
