The NAHT headteachers' union wants politicians to accept an amendment to the Digital Economy Bill that would allow local councils to share the benefit data they hold with schools.
The change would mean eligible children would be automatically enrolled to receive free school meals – boosting the pupil premium funding which schools receive for such children as a result.
Currently, parents have to apply to their local authority to get the meals for their child.
However, Labour MP Louise Haigh has tabled an amendment which explicitly sets out that councils can share with schools the data they hold on the names of pupils living in households claiming council tax benefit, housing benefit, and other local authority administered welfare.
Russell Hobby, the general secretary of the NAHT, said the amendment had the potential to improve the uptake of free school meals.
“We know that not all children who are eligible for free school meals claim them,” he said.
“The government can change that by accepting this amendment today.”
Mr Hobby said that as well as ensuring more children got the free meals they are entitled to, the amendment would increase the funding schools receive through the pupil premium.
“At a time when school budgets are being pushed beyond breaking point, and an autumn statement delivers nothing beyond the government’s project of grammar schools, this change could deliver much needed support and money for children and schools,” he said.
The NAHT said the amendment could reverse a recent "drop off" in the number of children claiming free school meals from year three onwards – the "cliff edge" at which entitlement to universal infant free school meals ends.
The amendment instructs councils to take "all reasonable steps to preserve the confidentiality and right to privacy of qualifying children and their parents or guardians" when sharing the benefits information.