The study, by BBC Scotland, uses Freedom of Information data to show that the payments available to poorer families vary from £20 to £110 across Scotland, with Angus Council paying the lowest grants and West Lothian the highest.
Scottish councils have a statutory duty under the 1980 Education Act to provide support to enable parents who could not otherwise afford it to clothe their children properly for school.
Both the criteria and the sum are for individual councils to determine, but in 2009 a broad-based working group set up by the Scottish Government recommended a minimum grant of £70 per child, subject to regular review.
Six years on, according to the BBC survey, only six authorities are meeting or exceeding even that initial minimum. Just eight have increased payments since the working party reported, and two – Angus and South Ayrshire – have cut them.
Over the past decade, the total paid out across Scotland in school clothing grants has fallen from £9m to £6.7m.
The figures were described as “hugely disappointing” by John Dickie, head of the Child Poverty Action Group in Scotland, who was a member of the 2009 working group.
“We know of siblings that end up having to share a gym kit, and of families struggling to replace clothes as they're worn out or where kids have grown out of them,” Dickie said.
“Some families are struggling to have enough items of clothing to just get through the week if something needs washing.”
