Families are "dreading Christmas" because they don't know where they will find the money to buy presents and put a Turkey dinner on the table, teachers have warned.
It comes amid growing concerns that many children are turning up to school hungry and teachers are dipping into their own pockets to pay for food for their students.
Meanwhile, "cohorts of children" are "disappearing" from schools across the country, having their education disrupted, as they move homes because of high rents and benefit cuts, teachers warned.
Christine Blower, general secretary of the National Union of Teachers (NUT), said that working families hit by cuts are finding themselves in severe poverty and branded this an "utter disgrace".
She told The People's Assembly in London: "Life is hard for thousands of families and thousands of individuals who are on the receiving end of the cuts in welfare benefits and the cuts in services and whose lives feature continued visits to food banks and fear of the bedroom tax."
Borrowing an approach from Labour leader Jeremy Corbyn, who has used the stories of ordinary people to articulate his questions in the new-look PMQs, Ms Blower told the Assembly about a mother called Rebecca.
Quoting Rebecca, she said: "My husband and I are both in full time employment but we still struggle.
"Anyone bringing up children will know how heartbreaking it is to have to say no to something a child wants.
"I dread Christmas. I hate it when their trainers have got a hole in, or they bring another letter home from school saying they need money for a trip.
"Food seems to be the only expense we have immediate control over, so that budget gets squeezed. And our home isn't as warm as we would like it to be during the winter."
Ms Blower added: "It's an utter disgrace for anybody to live like that, let alone two people working.
"It beggars belief."
She said that for some pupils in Britain, the free school meal they get for lunch may be their only hot meal of the day.
And she raised concerns about "disappearing cohorts of children" who are leaving their schools because their parents are having to move to different, cheaper areas, amid sky-high rents and cuts to benefits.
She said: "Many NUT members support children who arrive in their classroom every morning hungry. They may not have eaten anything since their free school lunch the previous day and some of them might not even be eligible for a free school lunch.
"We have members who take food into schools every day so children are not too hungry to learn.
"Many teachers too are now talking about the disappearing cohorts of children. These are families who have moved from their homes in established communities because their parents can no longer afford to live in those homes - either because of the bedroom tax, or because of the obscene levels of rent people are being expected to pay."