Parental involvement in schools is being stymied by a lack of clarity about child protection procedures and criminal records checks.
And governors seem to think parents are far more heavily involved with their schools than the parents do.
A survey of 384 parents and 109 governors, carried out by the charity Children in Wales, found schools gave police checks as a reason for not formally involving parents in some activities.
The report says schools need more guidance on how child protection procedures apply to help overcome uncertainty about how to deal with parents - and governors - who do not regularly help.
It found that nearly half of all parents were not formally involved in their child's school, although governors seemed to think 95 per cent were.
Single parents, and those with older or disabled children, were less likely to be involved.
Tony Ivens, Children in Wales's fatherhood development officer, was unable to explain the discrepancy between parents and governors' levels of involvement, and suggested further research was needed.
But he said it was a concern that schools were using Criminal Records Bureau checks as a reason for not involving parents.
"You can't have parents working with children without checks being made.
But it's a shame if that's stopping them, because we know from academic research the enormous benefits to children of having parents involved," he said.
"The evidence shows clearly that parents are key in the education of their children. Where there is good parental involvement, behaviour and academic achievement are all much better."
The survey found that parents' preferred method of involvement was learning alongside their child in school - followed by a parent forum or council, school trips, and supporting sports teams. However, fewer than one in 10 was able to do this.
The results of the survey were presented at a conference this week at University Hall, Cardiff, which also heard from experts, practitioners and politicians working with parents and schools.
Geoff Cresswell, headteacher of Hawthorn junior school, Cardiff, told delegates how a family learning programme had helped improve motivation and attititude, and engaged mums and dads as well as grandparents and uncles.
The school won a national award this year for its work in linking its families with families of children at other European schools.
Mr Cresswell said the family learning programme, which involved working with the city's adult education services as well as the local community, had been set up to support children who were not learning as much as they should. It started running after-school IT sessions for families five years ago.
"The two biggest barriers to learning are motivation and children's attitude to their learning," he said. "If you get a child who doesn't want to know, you can have Mount Krakatoa exploding on the whiteboard and it doesn't matter.
"It's an issue of internal motivation. One other thing is opportunity - are we as a school providing it? That's where family learning comes in because it hits on those two areas powerfully.
"Not only are families learning together, the children are learning from and with the adults, and the adults are learning from the children.
"It's this - that learning is for everybody, for life - that is so powerful as a motivation for these families and children."