Nicola Sturgeon has come under fire on education despite her insistence that improving the system for youngsters would be her "number one priority" if the SNP wins the Holyrood elections.

The First Minister and SNP leader said her party would give both teachers and parents a "bigger role" in decisions at schools.

She reiterated her commitment to tackle the attainment gap between rich and poor pupils, and highlighted SNP plans to invest an extra £750 million over the next parliament to help achieve this.

But Labour has claimed the SNP manifesto for the May 5 election fails to include a specific commitment to protect education funding.

Leader Kezia Dugdale said her party would do that and called on the SNP leader to make the same pledge.

Liberal Democrat leader Willie Rennie questioned why statistics on numeracy and literacy in Scotland had not been published as usual this year.

For the past five years the results of the Scottish Survey of Literacy and Numeracy have been published in either March or April, but this year they are not due to be published until the end of May, according to the Scottish Government website.

Mr Rennie said: "The First Minister has said education is her number one priority. But the results of the last two of these surveys have shown overall literacy and numeracy standards are slipping, and the attainment gap is widening.

"It seems convenient that we're being expected to wait more than a month longer than ever before to get sight of the most up-to-date statistics on literacy and numeracy. But that is the kind of jiggery-pokery we've come to expect from the SNP."

Ms Dugdale said: "In her manifesto yesterday, Nicola Sturgeon offered protection for the NHS budget, but not for education. This is not a technical detail.

"If the SNP leader does not make this commitment in simple terms, it means she plans to cut education spending in real terms.

"So, here is a simple challenge to Nicola Sturgeon - I'll protect education spending in real terms. Will you?"

Labour plans to increase the basic rate of income tax in Scotland by 1p and would also restore the 50p top rate for the highest earners, with the party promising to invest the money this would raise into local services.

Ms Sturgeon, who was campaigning in the Galloway and West Dumfries constituency, said: "The goal of the SNP will be to substantially close the attainment gap in the next Parliament and to eliminate it within a decade.

"I have set out ambitious proposals to ensure that every child has the chance to succeed in life and if re-elected as first minister I will ask to be judged on my success in achieving this.

"From the earliest years until adulthood, improving Scotland's education system should be the number one priority of the next Scottish government.

"That's why, alongside a strong national framework, I want to see parents and teachers, who have some of the best ideas about how to support children's education, able to play a bigger role in the life of their schools."

Conservative leader Ruth Davidson said she would welcome handing more power to teachers and parents but cautioned: "So often in the past nine years we have seen them (SNP) with great intentions but not following through because they have been too distracted by running another referendum."

The Tory, who was visiting Colinton Nursery in Edinburgh, said her party wanted to see improvements "right across the board" in education.

"That means instead of putting all of the money into free childcare for three and four-year-olds, it means extending that down to more disadvantaged one and two-year-olds," she argued.

"At school level itself it is about empowering teachers and school leavers to take more of their own decisions rather than having them held in central and local government."

Green education spokeswoman Isla O'Reilly, who is standing for the the Highlands and Islands region, said: "Closing the attainment gap is important but the SNP's return to national testing, encouraged by Labour and the Tories, is not what Scotland's young people need.

"Class sizes are the biggest they've been since 2007 and the Scottish Greens are committed to recruiting 4,000 more teachers over the next parliament to ensure teachers have time to teach."

An SNP spokesman said: "As usual, Labour are playing catch-up - we have already set out plans which will see spending on schools and nurseries increase in real terms over the next five years.

"Our ambition for the next parliament includes investing an additional £750 million in raising attainment and improving schools, with the bulk of this money going straight to headteachers.

"We will almost double childcare provision by the end of the parliament, helping parents get back to work and giving children the best start to their education.

"On colleges and universities we will take no lessons whatsoever from a Labour Party that introduced backdoor tuition fees on Scotland's students - we have scrapped those fees and will keep university free while also protecting college places."

The Scottish Government said the publication date for the Scottish Survey of Literacy and Numeracy "varies from year to year" and added the date of publication had been announced well before the election in line with the code of practice for official statistics.