Teachers' unions have defended the use of unofficial exclusions after the practice was criticised by the children's commissioner for Wales.
Keith Towler said in his first report that pupils and parents must be told that such exclusions - which are informal agreements between schools and parents to find alternative education provision for disruptive pupils - are not legally binding.
He also warned that the practice risks children not getting the extra help that they need, and he called for more guidance to be issued to local education authorities.
But some unions saw Mr Towler's comments as naive. David Evans, secretary of the National Union of Teachers Cymru, said Mr Towler had failed to grasp what was happening in the real world, particularly on unofficial exclusions.
"There are very good reasons why a school might go down the unofficial route," he said. "Things aren't black and white. We need to recognise that and look at what's realistic."
The NUT Cymru also saw the commissioner as "straying out of his remit" after he announced in the report that his office was planning to send out "pointers" to teachers on what helps children to learn, after his consultation with pupils.
Mr Towler's line on unofficial exclusion follows condemnation of the practice by the Assembly government and in the National Behaviour and Attendance Review report, published earlier this year.
Critics believe the practice could leave young people "roaming the streets" and likely to go off the rails as they end up at home without full educational provision.
Permanent exclusions in Wales were down a third in 2006-07, according to Assembly government figures. This is directly attributable to the rise in school and local authority-managed exclusions.
Following the release of the behaviour report, it was recommended that schools with high numbers of permanent exclusions should be investigated by Estyn.
But Dr Phil Dixon, director of teachers' union ATL Cymru, said unofficial exclusions were made "with the interests of all the children at heart".
"If schools are under pressure not to do it, we'll see a rise in formal exclusions, which will stigmatise those pupils," he said.
"It's like giving the children a yellow card and a second chance."
Elsewhere in his report, Mr Towler said he wanted teachers and pupils to help mould schools into places "where children want to be".
Children and young people want adults to improve the learning experience for them, he said, and to this end his team is collecting views on what makes a good teacher and a great lesson. Ultimately, they will produce material giving teachers pointers on what children value.
But Mr Evans objected to the pointers, saying: "Good teachers understand the learning needs of the child." "They listen to children and know what makes them tick," he said.
However, Dr Dixon said: "I think good teachers will welcome it. It could be more useful than diktats from central government."
Mr Towler's report stresses the importance of constant child consultation over matters from school closures to changes in school food.