Anti-poverty campaigners are calling on the Scottish government to introduce a minimum school clothing grant.
Currently the amount parents on low incomes receive to buy uniforms is at the discretion of individual councils.
A study by BBC Scotland last year found parents in Angus were offered just Â£20, while those in West Lothian received Â£110.
The Scottish government said the deputy first minister would meet with local authorities to discuss a minimum grant.
Figures taken from a forthcoming publication produced by Glasgow Centre for Population Health suggested the cost of providing a school uniform for children in Scotland was about Â£129.
Child Poverty Bill
Ahead of pupils returning to school after the summer holidays, charities – the Child Poverty Action Group, the Poverty Truth Commission and One Parent Families Scotland – said they wanted parents to take to social media to share their views on the true cost of clothing a child for school.
They are also asking parents to write to their MSPs, highlighting the need for a minimum school clothing grant for the whole of Scotland.
Earlier this year, Scottish ministers gained the power to introduce a minimum school clothing grant through an amendment to the Education (Scotland) Act 2016.
A spokeswomen said the Scottish government was launching a consultation on their Child Poverty Bill on Monday.
She said the bill, to be introduced next year, would build on existing work, and form part of the government’s overall approach to tackling poverty and inequality in Scotland.
She added: “The school clothing grants provision, introduced in the Education Scotland Act 2016, will provide welcome support for families who need it most, ensuring that all children and young people have suitable clothing to enable them to learn and thrive at school.
“The deputy first minister will shortly be meeting with Cosla to discuss the school clothing grant and agree eligibility criteria and a minimum grant level to ensure those families across Scotland who need support receive it.”
John Dickie, director of CPAG in Scotland said: “Though the responsibility to ensure school clothing grants are adequate ultimately lies with local authorities, the Scottish government has a golden opportunity to set a minimum rate for the whole of Scotland, helping to ensure every child can return to school feeling comfortable, confident and ready to learn.
“If government is serious about closing the attainment gap it is small but significant measures like this that can make all the difference.”
Satwat Rehman, head of One Parent Families Scotland, added: “The cost of school uniforms is leaving many children in low income families at risk of bullying and embarrassment because they are sent to school in ill-fitting clothes or in clothes which don’t meet the dress code.
“Parents are paying hundreds of pounds for school uniforms, with many poor having to cut back on essentials in order to afford them.”