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.
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.
At Strathallan in Perthshire only 0.9% of the school roll received a 100% award.
At Belhaven Hill School in East Lothian only one pupil got a 100% bursary in 2011-2012.
The same was true at Clifton Hall in Edinburgh, which charges up to £9255 a year. At Craigclowan, near Perth, around 14.1% of the school roll benefited from bursaries, but no pupil received more than 80% of the total fee.
At the Edinburgh Steiner school, bursaries were generally offered at between 33% or 40% of the total fee, with no pupil getting 100% support.
At the all-girls Kilgraston school, more than one- quarter of pupils received support, but none enjoyed a full bursary.
An OSCR spokesman 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."