"I do not think it is credible in what is a public service to not make information available to parents," David Bell told an audience at the Social Market Foundation think-tank in London.
League tables of test results for 11, 14 and 16-year-olds are published in England but not Wales. Seven-year-olds are formally tested in England, but Wales dropped key stage 1 Sats in 2001.
The Daugherty report on assessment, commissioned by the Welsh Assembly government and published last week, recommended that tests for 11 and 14-year-olds in Wales should also be phased out. Moderated teacher assessment would be used to judge pupils' progress instead.
Asked by Phil Collins, SMF director, if he believes Welsh parents are being let down, Mr Bell said: "Yes, I categorically do."
It is not enough to let schools tell parents how their children are progressing, he warned. Policy-makers must not be driven only by professionals' opinions about what should be published.
Mr Bell was taking part in an unscripted "conversation" with policy-makers, practitioners and journalists at the SMF which also covered performance pay, school admissions and inspection.
A spokeswoman for education minister Jane Davidson said consultation on abolishing performance tables in Wales had confirmed they were incomplete, divisive and demoralising to staff, and sometimes damaging to pupils.
She added: "The standards in our primary schools continue to improve and are higher than in England without us ever having published tables.
"Schools will continue to publish their results in prospectuses. Parents will not be in the dark."