Students and teachers at Yarralumla Primary School have been locked out of some classrooms since the start of Term 3 after high levels of lead were detected in at least 11 rooms.
Windows were replaced in eight classrooms in the July school holidays as part of remediating lead paint. Cleaning at the end of the work discovered unsafe levels of lead contamination.
After an assessment of other areas of the school was conducted, three more spaces were found to have elevated levels of lead.
Students enrolled in Yarralumla preschool, the Montessori school and 3/4 primary school classes have been forced to learn in alternate spaces around the school and spend long periods of time outside.
The after school care program has also been relocated while specialist environmental cleaning is being conducted.
Education Minister Yvette Berry said the Education Directorate expected that students and staff would be able to return to their classrooms later this month.
"I understand this is not an ideal situation, but of course the safety of students and staff is the priority and so the impacted areas will not reopen until they are cleared as being safe to occupy.
"Classes have been temporarily relocated to alternative spaces in the school to make sure students' learning can continue with minimal disruption."
Parents were advised on Friday that initial cleaning efforts in eight classrooms did not result in a significant reduction in lead levels so an advanced environmental cleaning process had begun.
On Tuesday, parents were told that high levels of lead were found high on the tops of cupboards in three more rooms and that staff and students would not have access to classrooms until next week.
Montessori parents were advised by email that staff did not have access to a kitchen and the Yarralumla pre-school children would be sharing a toilet block because their regular toilets had not been passed as safe.
The cleaning work is being completed by International Asbestos Removals Pty Ltd and involves a process of vacuuming surfaces with a HEPA filtered vacuum and leaving it for one hour for dust to settle.
Then surfaces are vigorously scrubbed with a sugar soap solution, a microfiber cloth and a three-bucket solution.
The surface is then rinsed with clean water and wiped dry with clean cloths.
Cleaning items are then disposed of in sealed plastic bags. When the surface is dry, it is vacuumed a second time.
The ACT Education Directorate commissioned Robson Environmental to conduct a study on lead paint and asbestos at Yarralumla Primary School in April 2019.
The lead paint assessment recommended that immediate action should be taken to reduce exposure risk. The Yarralumla Gambarri and Preschool and the after school care building were identified as areas of high risk.
A spokesperson for Ms Berry said Robson had confirmed at the time that the school had been safe to occupy.
"Lead in Yarralumla has been managed appropriately with expert advice."