Two in five parents said Cornwall schools were not dealing with bullying quickly and effectively, new figures show.
It comes as the Anti-Bullying Alliance, which coordinates Anti-Bullying Week each year, said staff must be better equipped at tackling bullying to lessen the serious impact it has on children.
Ofsted figures for the year to September 2023 show 5,826 parents were asked if their child has been bullied and whether the school dealt with the bullying "quickly and effectively".
Of the 2,260 parents that said the question was relevant to them, 40% disagreed or strongly disagreed that the school handled the bullying effectively.
Across England, 32% of parents said their child's school did not deal with bullying well.
The data covers private and public nurseries, primary schools, secondary schools and special schools.
Martha Evans, director of the Anti-Bullying Alliance said bullying behaviour is a "persistent problem" in schools.
She added: "We know that almost a quarter of children say they are being bullied frequently face-to-face, so it is unacceptable that understanding how to deal with bullying isn’t a mandatory part of initial teacher training."
"There are many examples of school staff who do a great job for the children that rely on them, but we must do more," she said.
"If we get better at equipping staff to root out the problem, take a whole-school approach to tackling bullying, and make sure there is a senior teacher leading the way, then the serious implications of being bullied can be lessened."
The figures also showed 11% of parents across England said their children were not happy in their school and 9% did not feel safe in the schools.
In Cornwall, 18% of parents said their child was not happy at their school while 15% said their kid did not feel safe.
David Johnston, minister for children, families and wellbeing said: "Bullying is never acceptable, which is why this government is committed to working with schools to create good behaviour cultures and to improve approaches to tackling bullying.
"We’ve created behaviour hubs across the country, included teaching respect and inclusivity as part of the RHSE curriculum and provided more than £3m of funding to anti-bullying organisations to support their vital work."