Talented teachers could be lost from the profession unless classroom violence is tackled, the Conservatives have warned.
Figures obtained by the party show the number of exclusions for assaults on school staff has risen by 50 per cent over the past six years, up from 793 in 200405 to 1,186 in 200910.
The figures are in stark contrast to the situation in England. It was revealed last week that the number of exclusions for attacks on staff in England fell by 40 per cent over the three years to 200910.
Out of Wales's 22 local authorities, 18 have seen increases in the number of exclusions since 200405 and only three have seen decreases.
Shadow education minister Angela Burns said: "While this kind of behaviour is obviously not a problem in every classroom or every school, where it happens we are in danger of losing talented teachers from the profession."
Andrew RT Davies, the party's leader in Wales, called the figures "incredibly worrying".
"Teachers and children have every right to expect their schools to be a safe and respectful environment. It's quite clear there is an awful lot of work to do just to get this problem back to 2004 levels."
An assault on a member of school staff is only recorded centrally if a pupil is excluded as a result, and the figures include pupils excluded more than once for violence in the same year, so it is unclear whether incidents of violence are actually on the increase.
Behaviour expert Professor Ken Reid said the rise was down to a zero- tolerance approach to violence from schools and the actions of a minority of "out-of-control" children.
"There are a growing number of schools that are simply not prepared to put up with serious misbehaviour," said Professor Reid, who led the groundbreaking National Behaviour and Attendance Review for the Welsh Government.
"While schools try to be inclusive and not exclude unless it's a last resort, if there's violence against staff, headteachers have very few options left.
"There is also a small minority of pupils who are completely out of control, at home, in their neighbourhood and, equally, at school. They bring that behaviour into the classroom. It's the same culture of disaffection which has led to the riots in London and elsewhere this week."
Professor Reid said lack of proper discipline is also an issue in some schools. "Some teachers are very confused about what they can and cannot do when faced with misbehaving, violent pupils," he said.
The Conservatives said the problem should be tackled at Government and community level, and called for parents and teachers to work together to create "safe and stable" school environments.
The Welsh Government has recently introduced new powers and duties for school discipline, parental responsibility and exclusion, including revised guidance on the use of force to control or restrain pupils.
A spokeswoman said: "We do not tolerate violence and aggression in schools and colleges, against teachers or pupils . The measures we have introduced show how determined we are to stamp out violence in all forms from our schools."
Original headline: Classroom violence could deter talented teachers, warn Conservatives