Oversized classes and inadequate staffing levels are hindering teachers’ capacity to support children with special educational needs and disabilities (Send), according to a large survey of state school teachers in England.

Nine out of 10 (89%) of the 10,000 teachers who took part in the poll by the National Education Union (NEU), before its annual conference in Brighton which starts on Monday, said class sizes were too big to be “properly inclusive”.

Four out of five (83%) said insufficient numbers of support staff in the classroom created a barrier to inclusion, while seven out of 10 (69%) said lack of access to specialist services was also a problem.

One teacher described the plight of a pupil trapped on a waiting list. “I have a suicidal boy in my class who is on a six-month waitlist just to be ‘seen’ by a specialist,” they said. “How can this be?”

Just one in five (22%) respondents said they were confident that referring a pupil for Send assessment, diagnosis or support would get them the help they need, while nine in 10 (88%) said an “inappropriate” curriculum was a barrier to some extent.

The findings come shortly after the government published a white paper, laying out its plans to improve inclusion in mainstream schools to ensure children with Send are better supported, as part of a radical overhaul of the special educational needs system.

The NEU general secretary, Daniel Kebede, warned that mainstream schools are not resourced or staffed to cope with current levels of need and said additional money promised by the government to fund the changes was insufficient.

“While the NEU supports many of the principles in the white paper, this survey of teachers demonstrates that mainstream schools are simply not resourced or staffed to cope with the current level of pupil need,” he said.

Schools would need “significantly more resources” to realise the government’s ambitions, Kebede added. Under current funding plans, the inclusion grant would amount to £13,000 for an average primary school – equivalent to one part-time teaching assistant.

Under the proposals, laid out last month by the education secretary, Bridget Phillipson, mainstream schools in England will assess pupils with special needs and draw up individual support plans, creating additional workload, before the changes take full effect in 2029-30.

The aim is to extend support to many of the 1.3 million children in state schools identified as having special needs who do not have the education, health and care plans (EHCPs) currently required for individualised support. In future, only children with the most complex needs will qualify for EHCPs.

The Department for Education (DfE) will provide schools and colleges with £1.6bn over three years to improve inclusion. A further £1.8bn will fund local authorities to hire specialists for schools to call on and £200m will pay for additional teacher training.

A DfE spokesperson said: “This government is fiercely ambitious for every single child and that’s why we’ve brought forward once-in-a-generation Send reforms to put inclusion at the heart of education.

“We’re backing schools and teachers with more resource and expertise through our £4bn investment to improve teacher and support staff training on Send, make sure every education setting has easy access to Send specialists, and funding directly for schools to make changes that improve inclusion.”