WA's population explosion has been underscored by revelations that public schools had to take 8000 more students in 2012 than forecast in May's State Budget.
Treasurer Troy Buswell had to top up the Education Department's funding with an extra $55 million in last week's midyear financial review to cover the unexpected growth in enrolments and other cost pressures.
That money is on top of an extra $92 million in the Budget in May for the same reasons.
The midyear review says the new money is to employ 681 more full-time education staff at an expected cost of $332 million over the four years of the forward estimates to 2015-16.
The Education Department predicts 273,220 students will enrol in public schools for 2013, up 5100 from 2012.
The Health Department's budget also had to be topped up $85 million to meet "higher than anticipated" demand for hospital services, including an extra $20 million for elective surgery.
There was no additional provision in the mid-year review for extra hospital demand over the three "out years" to 2015-16.
WA's population grew 3.3 per cent in the year to June, according to the Australian Bureau of Statistics, or about 1500 people a week.
Mr Buswell said about two-thirds of those people came from overseas.
"Effectively, there are 8000 more students enrolled in Government schools now than we anticipated at the time of the Budget," Mr Buswell said.
"Eight-thousand (students) is a significant funding challenge."
The Government was forced to revise up its official population prediction of 2.3 per cent for 2012-13 to 2.8 per cent in the midyear review because of the continuing flow of people into WA.
Inflation, meanwhile, is projected at 3.25 per cent for Perth.
But State revenue is expected to grow just 0.4 per cent, mostly because of a fall in iron ore prices and a persistently high Australian dollar.
The high dollar diminishes the value of royalties paid to the Government, highlighting the challenge both sides of politics face as they seek to make responsible fiscal promises in the looming State election campaign.
Opposition Leader Mark McGowan said the jumps in population related spending were "a significant budgetary issue" but should have been foreseeable.
"We all know the State's population is growing and there is a baby boom going on," Mr McGowan said. "This is just indicative of the Government's woeful capacity to manage the Budget, which is having impacts all over the public sector."