The Office of the Scottish Charity Regulator (OSCR) gave pass marks to the schools after an investigation into whether the elite institutions – Ardvreck, Belhaven Hill, Clifton Hall, Craigclowan, Edinburgh Steiner, Kilgraston and Strathallan – do enough to qualify as charities
But Labour MSP Hugh Henry said the tiny amount of bursaries covering the full fee cast doubt on OSCR's criteria and conclusions.
Charitable status provides the schools with a raft of tax breaks, but is controversial in some quarters, as the fees charged by the institutions are seen as a barrier to access.
Public concern led to OSCR, the country's charity watchdog, identifying the private-school sector as a "high priority" for review in 2007.
OSCR recently found that three schools, including Fettes College in Edinburgh, failed to meet the "charity test" and gave them 18 months to comply with directions. OSCR passed 10 other schools, a decision that is now being questioned.
When assessing the benefit offered by the schools, OSCR looked at a range of factors, including activities provided free of charge and interaction with the local community, as well as mean-tested bursaries.
However, a close look at the figures on financial assistance has raised questions about these bursaries.
Strathallan in Perthshire spent 9.3% of its gross income in 2010-11 on targeted bursaries, covering 18.2% of pupils. But within this figure, only 0.9% of the school roll received a 100% award.
In 2011-12, Belhaven Hill School in East Lothian charged up to £18,825 in annual fees, and spent 5.3% of its gross income on means-tested bursaries. This covered 10.1% of the school roll, but only 0.8% – one pupil – got a 100% bursary.
Clifton Hall, Edinburgh charges up to £9255 a year. It was found to have spent 9.2% of its income on mean-tested fee support. Most of the bursaries amounted to 60% or less of the total fee. One pupil – or 0.8% of school roll – got a full award.
Craigclowan, near Perth, charges up to £9975 annually. In 2011-12, the school spent 6.8% of its gross income on means-tested bursaries. This benefited 14.1% of the school roll, but no pupil received more than 80% of the total fee.
At the Edinburgh Steiner school, 12.2% of pupils received means-tested support. The bursaries were "generally" offered at between 33% or 40% of the total fee, with no pupil getting 100% support in the year examined by the watchdog.
The all-girls Kilgraston school, which charges up to £24,705 a year, spent 11.7% of its gross income on means-tested bursaries. Although 28.5% of the roll received support, no pupil got a full bursary.
Finally, only one pupil out of 122 received a full bursary from Ardvreck School in Crieff. Beaconhurst Grange, Dollar Academy and the High School of Glasgow also passed – but none provided 100% support to more than 4% of pupils.
The statistics raise questions about whether the bursaries benefit low-income households, or if they instead act as discounts for middle-class families.
Henry said: "If these schools have managed to pass the test, then OSCR needs to tighten the eligibility criteria and the way it is applied."
Green MSP Alison Johnstone said: "On the face of it, it seems a rather easy test to past."
An OSCR spokesperson said: "The charity test isn't just about the number of pupils getting a 100% bursary. We look at the full scope of the charity's activity."