When Joanne Hetherington collected her 13-year-old daughter Ashleigh from school on Wednesday afternoon, she was shocked to see that, in the searing heat, Ashleigh was wearing a heavy jumper over her school dress.

The problem was that Ashleigh had grown during the summer holidays and now her school dress - the only one she has - was too tight. With two younger children in primary school, her husband out of work and a disability pension providing the family's only income, Ms Hetherington simply can't afford to buy her daughter a $67 school dress. So for the time being, Ashleigh's too-small dress, which Ms Hetherington washes out for her each night after school, will have to do.

Her voice quavers a little as she explains the impossible maths of it all. The family income is about $350 a week for two adults and three children. Ms Hetherington estimates that, if she were able to buy all the things her children need for school, it would cost her about $800. Each week, most of the $350 goes on her medication, utilities and rent - anything left over is spent on food. To have enough to pay for the groceries, she said, was "a luxury".

With barely a pause for breath after the financial strain of the Christmas period, many families like the Hetheringtons are struggling to pay back-to-school costs. Some parents are even going without food in an effort to pay for shoes, uniforms and transport cards for their children.

Charitable groups have reported huge increases in the number of calls from parents asking for help, and with their own resources stretched to the limit, many of those requests remain unanswered.

John Dalziel from the Salvation Army said the Salvos had experienced a 50 per cent increase in the number of calls from parents desperate for any help with uniforms, shoes, books and, in some cases, food. He said that while the reasons for the surge in demand were complex, more and more Victorian families were sliding below the poverty line, and the number of people surviving on disability pensions was increasing.

Then there is the problem of the education maintenance allowance (EMA). Each year the Victorian government gives low-income families an allowance of $254 for each secondary school student and $127 for each primary student to help with education costs. The allowance is paid in six-monthly instalments and is halved between the family and the child's school: the school's portion is to be put towards excursions, textbooks, stationery and general classroom needs.

However, some parents are now being pressured into signing their half of the EMA over to the school, and fear their children will be excluded from some activities and resources if they do not comply.

A spokeswoman for the Council for Single Mothers and their Children, Margo Northey, said she had heard of many instances of schools pressuring parents to sign over their EMA.

In one case, she said, not only was the EMA kept by the school, but parents were told there was a shortfall in the fee of $43. Parents were sent a letter saying that unless that difference was paid, their child would miss out on textbooks, diaries, library bags, Internet access, printing and photocopying.

In an effort to squeeze every last drop out of the family budget, Ms Northey said, some parents were going without food to pay education costs.

Deputy Director of Schools Don Tyrer said the government would frown on any instances where parents were being pressured by schools to relinquish their share of the EMA. "(Schools) can ask, but what they can't do is insist," he said.

Mr Tyrer said that schools must not ask to keep families' EMA as a way of gathering voluntary school fees."We have been explicit that this cannot be the case," he said.

If parents went to their schools and said that a voluntary fee was simply beyond their means, Mr Tyrer said, that should be the end of the story.

But for many low-income families, the line between the EMA and voluntary fee paying is not so clear, and the fear that their child will be excluded from some activities can provoke desperate measures.

Joanne Hetherington said she had received weekly letters from her youngest daughter's primary school asking her to pay voluntary fees. The fees are about $250 for primary school children. Even if she just paid for her two children at primary school, that would cost her another $500 on top of the $800 in back-to-school costs. All this on $350 a week.

Mr Dalziel said: "Voluntary school fees should be just that, and for families living below the poverty line it should be automatic that they don't pay those fees. When you think about people going without food so they can pay those fees, it's just outrageous."

The policy officer at the Victorian Council of Social Services, Gavin Dufty, called for the EMA to be returned to parents to enable them to buy essentials for their children during the school year without having to hand over half, or in some cases all, to the school.

In the meantime, Ms Hetherington will continue to work hard at finding ways to provide her children with their school needs and, hopefully, scrape together enough money to buy Ashleigh a dress that fits her.

"My kids are used to doing it tough. But they shouldn't have to do it tough all the time."

The Hetheringtons' back-to-school budget

• Income $350 a week
  
• Rent and medication $160 a week
  
• Utilities $100 a week
  
• Food $120 a week
  
• Back-to-school costs (uniforms, shoes, transport cards, books, stationery, art smocks, library bags, padlocks):
  • Ashleigh, year 8 $500 Daniel, year 3 $150
    
  • Brooke, year 1 $150
• Voluntary fees if the Hetheringtons were able to pay them:
  
  • Ashleigh $300
    
  • Daniel $250
    
  • Brooke $250