Flagship legislation aimed at closing the gap in achievement between pupils from rich and poor backgrounds is "simply not strong enough", the Scottish Government has been told.

Labour's Iain Gray said the part of the Education (Scotland) Bill setting out to achieve this must be strengthened before it becomes law.

He also told ministers it was "unfortunate" a key part of the proposals - the introduction of standardised testing in primary schools as part of a national improvement framework - was not yet in the legislation.

Education Secretary Angela Constance told MSPs at Holyrood the Bill "sends a strong signal nationally as well as locally of the value we place on ensuring all our children and young people receive the best education they can and achieve their full potential".

The legislation, if passed, will place a duty on local councils to make a priority of working towards closing the gap in educational outcomes between the most and least advantaged youngsters.

Ms Constance said it "proposes that councils and Scottish ministers prioritise reducing inequalities of outcome associated with socio-economic disadvantage when they take strategic decisions relating to education".

She stated: "At the nub of it, I want all of us, Scottish ministers, Parliament and local authorities, for that consideration of closing the attainment gap and the duties we all have to do that to be something more than just a passive recognition.

"While I accept legislation on its own is never the be all and end all, I do think given the impetus we share to really pick up the pace and close the attainment gap, anchoring that duty in legislation would be appropriate."

Mr Gray said Labour supported that aim, adding: "It is unacceptable that it remains the case that your educational outcomes depend more on your parents' income than any other factor."

While he said some progress had been made in tackling this problem, he said: "You are twice as likely to gain the entry qualifications for a top university if your parents are well-off than if they are poor. You are far more likely to leave school unable to read or write properly if your family is poor.

"We agree with the Scottish Government that the time has come for a concerted effort once again to address the unacceptable attainment gap in our education, that is the key purpose and principle behind this Bill and we support that."

Mr Gray stressed: "We do require the section of the Bill on equalities of outcome be strengthened and we will seek to do that at Stage 2.

"The requirement that education authorities have due regard to the desirability of reducing inequality of outcomes is simply not strong enough.

"It is unfortunate that perhaps the most important section of this Bill is not yet in it at all and we can not really properly discuss its proposals.

"That is, of course, the national improvement framework, which the government are currently consulting on.

"We support a change to the current position where almost all local authorities use different testing, particularly in primary school, but we do not support a return to league tables and high-risk national testing which leads to problems such as teaching to the test."

The Bill, if passed, will also require local authorities to have a chief education officer, with Ms Constance saying this change was being made "to ensure all councils continue to have senior officers to advise them on education issues".

All teachers in independent and grant-aided schools will require to be registered with the General Teaching Council for Scotland (GTCS), as they already do in local authority schools.

Ms Constance also announced the Government would make changes to the Bill to include a presumption in favour of Gaelic medium education at primaries, when councils are considering if there is reasonable demand for this.