Scottish government guidance says families on low incomes should be able to access a minimum of £120 a year for a primary pupil and £150 for a secondary pupil - figures which have not risen for three years.
But the eligibility for who gets the cash is set by local councils and varies widely across the country.
About 120,000 pupils receive the clothing grant but Jen, a single parent who lives in Balloch with her 10-year-old son, says she is angry and frustrated that she does not qualify.
She works 22 hours a week in a care home but struggles to cover her bills.
However, her salary leaves her above the £933 a month threshold for the school uniform grant set by West Dunbartonshire Council.
Just a few miles up the road in the Stirling Council area, Jen's income would put her well below its £1,851 threshold and she would qualify for the grant.
The majority of Scotland's councils stop the grant when families on Universal Credit have earnings of over £850 a month, the same criteria that is used for free school meals.
But eight councils allow people on much higher incomes to claim the allowance, with some also using council tax rebate or housing benefit as criteria.