Engineers have recommended demolishing the historic facade of Mt Lawley Primary School, saying structural damage makes it impossible to save the heritage building that was mostly destroyed by fire last month.
Police on Tuesday charged two teenagers over the fire which caused about $9 million damage.
Premier Colin Barnett said after the fire that he hoped the facade could be retained, but the Education Department has since told the school a structural engineer's report had found many of the remaining walls were unstable and deemed to be unsafe.
Architects would be asked to look at ways to keep some elements of the old school in the rebuild, such as the entrance and windows, and reuse bricks for external paving or artwork.
Mt Lawley Society president Bruce Wooldridge said it strongly supported keeping the facade and structural assessments should be made public.
Education Department infrastructure executive director John Fischer said the school was likely to be demolished in two weeks.
Police charged a 16-year-old girl with trespass and two boys, aged 15 and 16, with criminal damage by fire. The youths allegedly set fire to chairs under a veranda in the school courtyard.
The blaze engulfed a big section of the school.
The teenagers are due in Perth Children's Court on August 31.
Students have been moved to Mt Lawley High School while their campus is rebuilt. Their interim classrooms were built on a soccer pitch at the high school in just 13 days.
Education Minister Peter Collier said he was pleased charges had been laid.
"It will ultimately provide a bit of solace to the Mt Lawley Primary School community and that is important," he said.