At least one child in every primary school classroom who persistently defies authority, loses their temper and annoys other students could have a condition known as oppositional defiant disorder.
The disorder is defined as a repetitive pattern of disobedient and disruptive behaviours towards authority figures, which persists for at least six months.
Murdoch University senior lecturer in clinical psychology John Gardiner said ODD was "not rare", and could affect between six and 10 per cent of children.
"You're talking about one child in every classroom probably would meet the criteria in terms of needing additional support," he said.
Mr Gardiner said though he did not have any statistics, ODD could be becoming more prevalent in WA because children were expected to spend more time in structured settings, at school or day care, at a younger age than they used to be.
He said it was not a serious mental health problem.
"But of course it produces lots of distress for families and for child care centres, pre-primary and kindergarten rooms because they have social problems, difficulty in sharing, taking turns and obeying rules," he said.
It was important to pick ODD up early because without support some children could go on to develop conduct disorder, which leads to destructive behaviour such as lighting fires or cruelty to animals.
"It's probably one of the best predictors of later conduct problems, such as violence or juvenile delinquency," Mr Gardiner said.
School Psychologists' Association of WA president Stuart McKenzie said he suspected ODD was significantly under-diagnosed in WA.
Medication was not prescribed but it could be managed by recognising a child's triggers to stop conflict from escalating.
Telethon Institute for Child Health Research mental health researcher Monique Robinson said there had been debate over whether ODD was a real disorder, or just children being naughty.
She said diagnosis depended on the behaviour's frequency, intensity and duration and it was important for parents to realise it could be treated.
'It's probably one of the best predictors of later conduct problems, such as violence or juvenile delinquency.'"Murdoch University
lecturer *John Gardiner *