Headteachers want every school to have two more Inset days per year to cope with Labour's landmark special needs reforms.
Branch secretaries of the NAHT union, which mostly represents primary heads, say two extra teacher training days are needed to 'embed the changes'.
It would mean two more days off per year for pupils – with the total number of annual Inset days increasing from five to seven.
However, it could prove a headache for working parents, who would have to find extra childcare.
The proposal is contained in a motion put forward by the union's Solihull branch, and it is due to be debated at the annual NAHT conference in Belfast today.
If delegates vote the motion through, the NAHT will lobby ministers to create two extra statutory Inset days.
It comes after Education Secretary Bridget Phillipson unveiled White Paper plans in February to give mainstream schools more responsibility for special educational needs and disabilities (Send).
In future, all but the most severe cases of Send will be dealt with by mainstream schools, with teachers expected to adapt their teaching to accommodate these pupils.
Headteachers want every school to have two more Inset days per year to cope with Labour's landmark special needs reforms (file picture)
The motion urges union bosses to 'campaign for the introduction of two additional statutory Inset days each academic year, to support schools implementing and embedding the Government's ambitions for Send and curriculum reform.'
Inset stands for 'In-service Education and Training', with many schools laying on professional development and team meetings on these days.
The proposed two new days would be taken out of the 195 days teachers are contracted to work.
The Government has already said it will provide £200 million in funding by 2029 to train teachers in Send.
It is understood teachers will learn how to accommodate pupils with conditions such as autism and attention deficit hyperactivity disorder (ADHD).
Labour's overhaul of the system came in response to councils being almost bankrupted by the ballooning costs of funding Send pupils in special schools.
It comes after a number of schools have moved to a four-and-a-half day week to reduce budget pressures and prevent staff burnout.
Forest Gate Community School in London sends pupils home just after midday on a Friday to 'alleviate pressure' on teachers.
Schools are legally required to provide 190 days in any school year but these rules do not apply to academies.
The Department for Education has been contacted for comment.