Schools may be failing on obligations to make parents aware of a right to withdraw their children from religious lessons, a study has suggested.
Schools have had to alert parents that children can opt out of religious classes and assemblies since 2005.
But only 20% of parents asked by YouGov on behalf of the Humanist Society of Scotland said they had picked up this information from schools.
The society has sought assurances the issue is not being downplayed.
It is also concerned by reports that children who are taken out of religious lessons may be asked to simply sit and read, rather than given an activity to do.
The study found 39% of parents surveyed were not aware of the right to withdraw children from religions observance (RO) and religious and moral education (RME) and only 20% had originally been made aware of the right by their school.
The survey also found that although 18% of parents did not want religion in school, the majority would like their children to develop knowledge and understanding of a range of beliefs.
The report concluded: "Parents are not being made adequately aware of their right to withdraw.
"The frequency and style of RME and RO in schools is not being communicated to a significant proportion of parents."
YouGov surveyed 1,000 Scottish parents of children aged five to 16 to find out if they were aware of their rights.