Ngā Rauru tumuwhakarae Te Pahunga Marty Davis gave the karakia to start the occasion. Ngā Rauru also named the new outdoor space. It's called Tāne Whakapiripiri - Tāne's gathering place of nature and humanity.
Bushy Park education co-ordinator Robin Paul said groups of students used to sit on plastic chairs or carpet squares on the asphalt, and the classroom is a great improvement.
This year 2000 students, both primary and secondary, are expected to visit Bushy Park for lessons. Most of the region's schools use it, and some outside the region are starting to as well.
The students look for invertebrates in the wetland, and find out how to track predators in the forest. They learn about plants, birds and insects. Some lessons are in te reo Māori, and take in rongoa Māori and bush lore.
"Everything we do is outside. Our walls are the bush, and everything we do is hands-on," Mr Paul said.
Teaching staff from the Conservation Department, Whanganui museum, Sarjeant Gallery and Horizons Regional Council are all involved - but most of the work is done by volunteers.
The group is applying for funding to enable low decile schools to visit, and to pay a part or full-time educator at the sanctuary.
"If capacity increases like this we are going to be basically living out here all the time," Mr Paul said.
The construction of Tāne Whakapiripiri was done by the Rotary Club of Whanganui North. It has been in a partnership with Bushy Park for three years, and also built its wetland boardwalk and classroom and added shellrock paths and signs.
The work was funded by $54,000 from the Eleanor Burgess Trust. Rotary's next project will be on the sanctuary's entrance.
In other Bushy Park news, two new buildings have been added - a shed for volunteers and a workshop.
Volunteers will be working this winter to track the mice in the sanctuary, and find out whether they can be eradicated. They are also looking for the myrtle rust disease, which can attack rata, and collecting seed for a national seed bank.
The Lottery Grants Board has donated $100,000 toward an upgrade of the sanctuary's stables building, and the Bushy Park Trust is applying for more money to fix the leaking roof of the homestead.