Expulsions from Welsh secondary schools have risen for the first time in three years, with significant rises in punishments for assaulting staff and pupils.
Meanwhile, fixed-term exclusions have increased by 146 per cent since 199900, from 8,218 to 20,242 - and by 168 per cent for girls. Permanent exclusions of girls remain low compared to boys but at 91 are higher than they were 10 years ago.
Union leaders reiterated their concerns about the alarming rise in violence towards teachers in Welsh schools.
Of last year's 465 permanent exclusions, 13.3 per cent were for assault or violence towards staff (up from 49 to 62). Permanent exclusions for violence towards pupils rose slightly, but temporary bans rocketed from around 2,600 to nearly 3,500.
Both permanent and temporary exclusions rose for threatening or dangerous behaviour, but expulsions for verbal abuse and defiance of the rules were down.
Geraint Davies, secretary of classroom union the NASUWT Cymru, said: "I'm not surprised by these alarming increases, because our members are telling us that too many of our schools have become battlefields.
"It's about time society accepted that we have an increasing cohort of pupils who too often are prepared to use violence against adults or fellow pupils."
He believes pupils unwilling to conform to school rules should be educated via a network of pupil referral units. This should be a priority for the Assembly government's behaviour review, announced earlier this month, he said.
Brian Rowlands, secretary of the Association of School and College Leaders Cymru, said: "After many years in which exclusions have fallen, it is disappointing to see the trend reversed, especially as so many are designated special-needs pupils. This indicates that not enough provision is being made locally to support schools."
The association wants to see more work on improving home-school relations.
He added: "Schools try desperately to solve the problems resulting in exclusions. In the last resort, heads have to ensure the correct learning situations for co-operative pupils."
But others raised concerns about the rising number of female exclusions, the high proportion of special-needs pupils removed from Welsh schools, and the lack of support available.
Only 66 pupils returned to mainstream education in 20045 - compared with 103 out of 439 two years previously. Three out of 10 received only a few hours home tuition a week. Overall, 47 per cent of permanent and 38.5 per cent of temporary exclusions involved pupils with special needs.
The figures reinforce concerns raised last week (TES Cymru, March 17) about a shortage of education welfare officers able to help support at-risk children.
Professor Audrey Osler, of Leeds university, said: "Young people are blamed for society's problems. There is less recognition that those getting excluded for disciplinary reasons are often those who are failing to cope with the academic demands of school."
And she added: "Our research shows that the greatest single factor affecting a student's risk of exclusion is the school he or she attends.
There are significant differences between schools in the numbers of exclusions and the way difficulties are addressed."
An Assembly government spokeswoman said the rise in permanent exclusions from secondary schools was disappointing, but said rates were lower than in England and had fallen in Welsh primary and special schools. She suggested rising numbers of temporary exclusions could be the result of guidance for reducing permanent ones.