Other challenges will include working with a larger number of students, working with older students and potentially facing a high turnover of staff.
Ellery was welcomed with a pōwhiri on Friday.
"They have an amazingly strong and committed team here, but they are understaffed at the moment due to staff leaving and not being able to replace them," she said.
"I've got a huge focus on class sizes, we need to start addressing how many kids we're cramming into one class in front of one teacher."
Throughout five and a half years at Castlecliff School, on Cornfoot St, Ellery had a battled with the availability of relief teachers.
She said they restructured the school.
"It took a lot of work at Castlecliff, it's been a big journey and it was a journey that the team did together because we knew we needed to.
"Everyone taught in teams. The board invested heavily in very high quality support staff so if someone was sick or away, the pressure was off the reliever." The first day of term four will be a staff only day at WIS which will feature a presentation where Ellery can discuss these types of strategies.
They will start the term one staff member down, but Ellery didn't believe the staff changes were related to teacher negotiations with the Ministry of Education.
"I don't know a lot of the people who left, but I do understand that a lot were quite happy to leave teaching and had opportunities from partners moving to other centres.
"From what I can gather most of the ones who left in the last year were pretty legitimate, it was just unfortunate timing."
Her own thoughts on the negotiations are that the main focus should be about the teacher conditions, not pay.
"All they've dealt with is money and there's a huge claim on conditions, on staffing, on help with all of these behaviours that are coming through our schools," Ellery said.
"If the ministry had delivered on some of those conditions, or most of those conditions, teachers probably would have been a lot more responsive towards the pay offer."
On September 26 teachers and principals rejected the Government's latest collective agreement offers, following a strike on August 15.
Ellery said no matter what, teachers will continue to work as hard as they can and give students the best care possible.
"I want to keep the quality of teaching and learning as high as I can and to cater for as many needs as possible.
"At the moment, Whanganui Intermediate is the school of choice for intermediate kids and I want it to be the school of choice for the teachers as well."