In a letter to parents yesterday, Logan Park High School board of trustees presiding member Ronda Tokona said with "incredible sadness" she was informing parents that Ms Mouat died at home, peacefully on Saturday.
The school will be closed today and tomorrow as staff, students and the wider school community deal with the news.
Pupils, past pupils and parents have paid tribute to Ms Mouat on the Otago Daily Times and LPHS Facebook pages.
"An amazing teacher that I remember so many years later. RIP. You have made the world a better place," Nicola Colson wrote.
Stephanie Lloyd described Ms Mouat as a 'truly beautiful person. Always caring and compassionate".
On the school Facebook page ex-pupils shared their memories of Ms Mouat and devastation at the loss.
"Ms Mouat was a beautiful teacher. I'm so sorry to hear this news," Dunedin musician Nadia Reid wrote.
"Kristan had a huge influence on me all through high school and was one of the most supportive figures I could have had at a time when I really needed it to flourish. She made my time at Logan Park a formative and unforgettably positive experience," ex-pupil George Sabonadière wrote.
Dunedin MP Michael Woodhouse expressed his sadness at the news: "I met with Peter and Kristan just last Friday and was really impressed with their partnership and leadership. My sincere condolences to her family and the wider LPHS whanau."
In the board of trustees letter to parents 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."
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.
