A new study says one in five primary school boys exhibit emotional and behavioural problems.

A team from Murdoch Children's Research Institute looked at 1,000 Australian school children aged eight to nine years old, whose parents completed a strengths-and-difficulties questionnaire to report on the wellbeing of their kids.

Emotional problems (e.g children having worries, fears, being easily scared, and seeming unhappy or sad) and behavioural problems (e.g acting out, temper tantrums, fighting, hyperactivity and restlessness) were reported in around 20 per cent of young boys.

The researchers say these boys were three times more likely to be rated by their teachers as having poor English or mathematical skills.

The NAPLAN results of boys with emotional or behavioural problems showed they are 12 months behind their classmates academically.

There also appeared to be a link between the early onset of puberty — for some boys as young as 7 or 8 — and behavioural problems in the classroom.

Lead researcher Dr Lisa Mundy said parents must learn to spot the warning signs of their child's distress.

She said key signs include sadness, anxiety and not wanting to go to school.

Interventions can be as simple as encouraging kids to express themselves, but; “If going through that you're still concerned, then at that point it's worth seeking help and just checking it's not anything more significant,” she said.