Of the 19 instances since 2019, 12 were classified as "notifiable" cases, Education Department director-general Tony Cook said in a state parliament estimates hearing on Thursday.

"In a number of those cases, the asbestos instance was discovering buried material from past instances, away from school classrooms (and) no exposure occurring outside of school hours time as well," he said.

Opposition education spokesman Christian Rowan said the "revelations" were proof the government "is losing control of safety in our schools".

"The management of asbestos has been a debacle at Sunnybank State High School," he said.

"Despite the asbestos incident being known and reported by staff at the school, it wasn't until more than two weeks later that a professional clean-up crew was dispatched, and parents and staff were notified."

The 12 instances equate to about two per cent of the 600 schools targeted by the government's air-conditioning program, but Mr Cook said the department "can absolutely improve our practices".

Improvements are being made through examining training and holding contractors to account, he said.

"Holding contractors to account for the fact that they're actually not following the guidelines which they've signed off and said they will follow," he said.

"And when necessary, suspending those contractors and not including them or engaging the in any work in the future."

Australian Associated Press