The number of children permanently excluded from schools in England has increased by more than 6%.
Pupils were most likely to be expelled at age 14
Government figures show there were 9,880 expulsions from primary, secondary and special needs schools in 2003-4, up from 9,290 in 2002-3.
The proportion of pupils expelled has also risen for the first time in three years, from 0.12% to 0.13%.
Persistent disruptive behaviour was the biggest cause, followed by physically assaulting a pupil.
The largest increase in expulsions was among secondary pupils, accounting for 8,320 - up from 7,690 in 2002-3.
The overall figure is the highest since 1998-9 but 2,420 fewer than in 1997-8.
Some 81% of expulsions in the latest figures are of boys, with 14-year-olds the largest single age group affected.
After disruptive behaviour (3,040) and assaults on pupils (1,720), assaulting an adult accounted for the most permanent exclusions - 1,190.
Then came verbal abuse or threatening behaviour towards an adult, on 1,130.
This is the first time the Department for Education and Skills has provided a breakdown of the reasons for expulsions.
Schools minister Jacqui Smith said: "The government has made tackling poor behaviour a major priority.
"We want a zero-tolerance approach to disruptive behaviour in all our schools on everything from backchat to bullying or violence.
"Schools must have clear and consistent boundaries for what is acceptable behaviour.
"Violence or verbal abuse against pupils and members of school staff will not be tolerated. I fully back heads who decide to remove or prosecute anyone - parent or pupil - who is behaving in an aggressive way."
Meanwhile, the number of suspensions from schools in 2003-4 was 344,510.
Parental appeals against exclusions increased from 1,070 to 1,130.
The proportion which succeeded was up slightly from 21.1% to 21.2%.
However the number of these which resulted in children returning to the same school fell from 150 to 130, or 71.3% to 57%.
The DfES said this was because of tougher guidelines for appeal panels, which ask them to look at the impact on other children when disruptive pupils are allowed back.
Ms Smith said: "There is a false notion that many heads are unwilling to exclude or that any exclusion they make will be overturned on appeal."
The figures showed that idea was "a nonsense", she added.
But shadow schools minister Mark Hoban said the overall figures were "further proof of the deteriorating standards of behaviour in our schools".
The government was "letting down" pupils, he added.
Liberal Democrat education spokesman Ed Davey said the government lacked an "overall strategy" for improving behaviour.
Steve Sinnott, general secretary of the National Union of Teachers, said: "Schools will not tolerate the deteriorating behaviour of a small number of young people.
"They will act to protect the right to an education of all other children and the right of the teachers to teach.
"These figures demonstrate that clear intention is being put into effect."
John Dunford, general secretary of the Secondary Heads Association, added: "The increase in the number of exclusions should be taken as a sign that heads are tackling serious disciplinary issues with all the weapons at their disposal."