Teachers are used to outbreaks of rudeness and defiance from their pupils, but are now saying parents are some of the worst offenders and affecting staff mental health, according to a headteachers’ union.

More than 90% of headteachers and other senior leaders said they had been on the receiving end of “challenging behaviour” from parents including rude or disrespectful responses, while 60% have had verbal abuse and threats within the past 12 months, according to the Association of School and College Leaders (ASCL).

More than three-quarters surveyed said the worsening parental behaviour was harming their mental health and wellbeing.

School leaders said parents were now more likely to disagree with a school’s handling of incidents, and would often dispute sanctions such as detentions or suspensions for misbehaviour or truancy.

Jo Rowley, a deputy headteacher from Stafford and ASCL’s president, wants the government to back a national campaign calling on parents to support their children’s school or college.

Rowley is expected to tell the ASCL’s national conference in Liverpool that “a minority of parents with unreasonable expectations and short tempers are a drain on time, energy, and resources”.

While most parents “work productively” with teachers, she will underline the importance of parents making complaints “in a polite and reasonable manner” to avoid conflict.

“Some parents are clearly struggling to deal with the pressures in their own lives, and their behaviour is very challenging,” Rowley will tell the conferences. “The huge amount of work and stress they generate detracts from other children, undermines behaviour policies, and contributes to the pressures which drive people out of teaching.”

Experienced headteachers said flashpoints included confiscating pupils’ mobile phones, with one parent accusing the school of theft and threatening to call the police. Other bitter disputes can come from turning down requests for pupils to take time off for family holidays in termtime.

More recently, heads said parents had been using AI to generate lengthy, legalistic complaints that required increasing amounts of time to administer.

Of the 1,700 school leaders surveyed by ASCL, 73% said subject access requests – statutory demands for personal data held by an institution – were being used by parents “in a challenging or excessive manner,” while more than half said they had experienced hostile or defamatory comments from parents on social media.

Martyn Oliver, Ofsted’s chief inspector, will also defend his organisation’s new inspection regime to the conference, explaining that more schools in England are receiving “needs attention” grades because of Ofsted’s “more exacting” standards. “Needs attention” is the fourth-lowest out of five on Ofsted’s new scale, which ranges from “exceptional” to “urgent improvement”.

Oliver is to say Ofsted will continue to highlight schools where it finds disadvantaged children “who are not making the strides that they should”. “We will never acquiesce to the quiet curse of low expectations that would see Ofsted prioritise context over outcomes for the most disadvantaged and vulnerable children.”

Bridget Phillipson, the education secretary, is expected to tell delegates: “The changes you have seen in your classrooms over the past decade – the poverty, the additional need, the technology – this is a new era of childhood, and it calls for a new era of education. An end to policy in parts. Instead, a village around the child. Every child. With schools as the beating heart of that support.”