The number of pupils expelled from schools in Wales has fallen to a record low, but there are concerns that too many unofficial exclusions are still taking place.
New figures show that permanent exclusions fell to just 213 last year, down from 241 in 200708 and the lowest figure since records began being kept by the Assembly government in 1999.
In the secondary sector, where the overwhelming majority of permanent exclusions are made, four local authorities excluded no pupils and a further four excluded fewer than five children last year.
But Professor Ken Reid, who chaired the groundbreaking National Behaviour and Attendance Review (NBAR) for the Assembly government, said the reduction may be due to increasing numbers of unofficial exclusions.
The Assembly government has urged schools and local authorities to "eradicate" the illegal practice as a result of NBAR's recommendations, but work carried out to assess the extent of the problem has not yet been made public.
Professor Reid said: "We still don't know how many unofficial exclusions are taking place.
"Exclusion used to be an easy option for schools, but since NBAR and the changes to the inspection process that is no longer the case.
"Schools know they are going to be monitored much more closely. In most cases schools have positively changed their practices, but we still don't know what unofficial arrangements are being made behind the scenes."
Dr Philip Dixon, director of the Association of Teachers and Lecturers Cymru, said: "On the face of it, the reduction looks positive, but we need to look more closely at unofficial exclusions and whether pupils are being displaced.
"Also, are staff having to put up with more behaviour problems from pupils who would ordinarily be excluded?
"Are we just pushing the problems back into schools?"
Last year children's charities Barnardo's Cymru and SNAP Cymru campaigned for an end to unofficial exclusions.
The government has also commissioned the organisations to carry out research with excluded pupils and their families.
Professor Reid also raised concerns after the number of excluded pupils left without education provision trebled last year to 39 - 18 per cent of the total - the highest figure since 200203.
He said: "Some of this group drift into crime and other social problems. We have an acute shortage of out-of-school places in Wales and very few alternative curriculum centres."
But an Assembly government spokesman said the rise was due to a change in the way the data was collected, and that the majority of those pupils would receive provision at a later point.
The government has acknowledged that many local authorities find it difficult to meet the guidance on providing full-time education for excluded pupils within 15 days, and officials will shortly start work to explore the barriers and to develop long-term solutions to the problem.