Shorten's sky-high schools pledge

Pie in the sky or the sky is the limit? Regardless of who you ask, splashing more money on school kids is up in the air.

Labor leader Bill Shorten has ramped up his campaign on schools policy unveiling his third education announcement of the week on Friday.

He's pledging to provide thousands of scholarships to boost the ranks of science, technology, engineering and maths teachers.

If elected Labor will provide $393 million for 25,000 places to encourage graduates to become teachers of STEM subjects.

Mr Shorten says it's about reversing the ranks of teachers unqualified in their subjects.

But it was also about showing kids the sky was the limit if you instilled confidence in them and properly trained teachers.

"In life there are some things which are beyond doubt," he told reporters in Sydney's inner west on Friday.

"A smart educated Australia will be a prosperous successful Australia, and that is beyond doubt."

However, the government is demanding to know how Labor plans to pay for its "pie in the sky" commitments.

Finance Minister Mathias Cormann has taken Mr Shorten to task over a promise earlier in the week that there would be an immediate economic boost from funding schools.

He told reporters on Friday that until Mr Shorten revealed how he planned to generate the money to pay for it, his pledges were meaningless.