Information gathered by the education ministry is at best faulty and at worst rigged, they say.
The ministry claims that 29,685 violent incidents broke out in public elementary, junior high and senior high schools in 1998 - less than one incident for every school in the country. Educators say this is a gross under-estimation of the problem.
Every year the ministry polls each local authority on such incidents. However, say critics, many schools and authorities do not, or are unwilling to, report facts which might reflect badly on the school and on its staff. Teachers believe that administrators are likely to doctor the facts when asked to submit reports on violence.
One county, Mie, decided to request full statements from every school for the first time in 1997 - and consequently saw the figure for violence shoot up from 18 incidents in 1996 to more than 1,000.
Shinji Fujikawa, of the Hiroshima Teachers Union, said: "If principals report the real figures of violent incidents which often break out in schools, the boards of education criticise them and brand them as incompetent. They are afraid of that and report false figures, which are much less."
Falsification is rife and the government knows it, say critics. But even going by government figures the escalation in violence and disruption in Japanese schools is alarming. The disputed 29,685 still represents a 25.7 per cent rise from the previous year.
Although Japan's schools have not always been the perfectly disciplined "quiet as the grave" places of learning of the popular imagination, the disruption and violence has surprised many.
Individual teachers speak increasingly of a great escalation in violence and the common emergence of "classroom collapse" - an unteachable, unruly and uncontrollable class.
What is most worrying, say the teachers, is that the culprits are not the usual delinquent minority but the more "ordinary" students. Even the government report bears this out.