The Education Directorate does not know how many teachers will be needed in coming years as teachers say they do not feel safe in classes of up to 60 students, an inquiry has been told.
Australian Education Union ACT branch officials fronted a Legislative Assembly hearing on Tuesday in response to an ACT Auditor General's report on teacher quality.
Secretary Patrick Judge said teacher shortages were causing many classes to be combined, putting staff at risk.
"I have to say if I was presented with sole responsibility for 60 high school students and it was a tricky class, I'd be scared. I'd be scared in that situation," Mr Judge said.
"And what our members tell us is that they are scared when they're faced with that situation, that they fear for their safety in those circumstances."
The union has been participating in a teacher shortage taskforce with the directorate, however Mr Judge said there were challenges due to a lack of data.
"It is a mystery to the AEU as to why we do not have projections for what number of staff we need, the teaching staff we need and in what specialisations we need them," Mr Judge said.
"We should be able to work that out on the basis of the same demographic data we have for students."
The union branch president Angela Burroughs said the government was working on a new system to capture teacher workforce data that should be ready by the end of this year.
The directorate will also be conducting exit surveys with staff to gather data on why they are leaving the profession.
Meanwhile, the hearing was told many staff did not have the time resources to do their job effectively.
Mr Judge said many teachers spent time assisting families with accessing support for their mental health, housing problems, medical issues and other welfare concerns.
"Our schools aren't resourced to deal with that sort of demand and we just don't have the staffing," Mr Judge said.
"And frankly, we don't necessarily have the expertise to be doing that sort of work."
Some union members reported not having a school library or staff room because the space has been converted to classrooms spaces while others were teaching in modified corridor spaces.
Ms Burroughs said not all staff had access to the technology they needed to do their work, especially casual teachers and learning support assistants.
"There's not enough devices to be able to give every staff member a device to be able to perform their work," she said.
The inquiry heard many teachers were unable to attend professional learning due to staffing shortages which were exacerbated by COVID-19 illness this year.