WELLINGTON, Dec 3 - Emergency services were called to the fire 4.40am on Sunday.
Police say they're treating the fire as unexplained and possibly suspicious.
"As a result of the fire more than 60 children have now been displaced from their classroom, and have lost valuable mementos and work," says Detective Sergeant Kelly Farrant.
"The classroom is only a little over a year old, and it's disappointing for the school and the children to end the year on a low note."
Police want to hear from anyone who was in the area from 9pm on Saturday and have released images of items of interest, including a scooter.
Green Bay School is a full primary state school catering for years zero to eight, located in west Auckland between New Lynn and Titirangi.