Scotland's classroom assistants receive "scandalously low wages" and are undervalued, according to an Equal Opportunities Commission (EOC) report.
There are about 15,000 classroom assistants in Scotland
The survey found classroom assistants are among the lowest paid local government workers, receiving between £7,000 and £10,000 a year.
A group of assistants gathered outside the Scottish Parliament to highlight their situation.
Scotland's councils said the criticism was exaggerated.
The EOC Scotland investigation found that 98% of Scotland's 15,000 classroom assistants are female.
The independent body warned local authorities they may be open to legal action by staff over pay.
The report said classroom assistants now play an established and vital role supporting pupils and teachers in Scotland's schools.
The survey indicated that for almost three-quarters of them, their role included taking groups of children for reading or maths.
Increasingly they work with children who are either disruptive or may need special care.
The report has called for a national action group, led by local authorities in partnership with the Scottish Executive and trades unions, to be set up to clarify the roles of the job.
EOC Scotland commissioner Rowena Arshad said: "This is a classic example of why the gender pay gap persists in Scotland today.
"It's time to put right the scandalously low pay that our classroom assistants receive for doing such a challenging and vital job in our schools.
"Their pay packet amounts to a national disgrace. Why do we pay women less to educate and look after children than we pay men to look after buildings?"
The survey questioned more than 2,000 classroom assistants, teachers and head teachers in primary schools.
It found hourly rates of pay ranged between £5.68 and £7.58.
There are four different levels of classroom assistant jobs but one or two pay rates currently exist in Scottish local authorities.
It also found 97% of the 934 teachers surveyed felt that pupils benefit from classroom assistants.
Among those protesting in the rain on Wednesday was Linda Hendry, who works as a learning assistant in an Edinburgh secondary school.
She said: ""We have a responsible job and we're quite lowly paid. I can only do my job because I've got a child and I get family tax credit, so children's education is being boosted or bolstered up by the tax credit system."
Edward Pajak, a learning assistant at Gracemount High School who is among the 2% of men who work in the profession, said he believed their wage remit went back to the days when it consisted mainly of nurses and mothers going in to help their children.
He added: "I think the whole status of learning and classroom assistants should be put on a more professional level, but it's not."
UNISON, which represents Scotland's classroom assistants, welcomed the report.
Legal officer Peter Hunter, said: "UNISON has consistently argued that these important members of the education team have been undervalued since they were placed on the lowest possible pay scale in 1999.
"We congratulate the EOC on their detailed work and welcome the report and call on the executive to fund the full compensation of women underpaid as a result."
Jim O'Neill of the Professional Association of Teachers Scotland, said: "We will be looking for a concerted effort by all concerned to raise the status, morale and remuneration of this growing band of people who are such an important part of the work in Scotland's schools."
Pat Watters, president of the council umbrella group Cosla, said classroom assistant roles are already being evaluated using a system agreed with trades unions.
"Of course classroom assistants have a right to equal pay," he said.
"Scottish councils recognise this and are using agreed methods of 'measuring' jobs to ensure it happens.
"The EOC has failed to understand how pay rates are directly agreed for local government staff."
Cosla said individual examples of classroom assistants working beyond their duties or long hours would be investigated.