Welfare reforms coming into effect today will force 68,000 single parents with children aged 10 or more to look for work or risk losing benefits.
Work and Pensions Secretary Yvette Cooper said that she was changing regulations to enable them to find work which fits around school times.
But single parents' campaign group Gingerbread accused the Government of failing to provide the necessary support to help them find work.
From today, lone parents whose youngest children are aged 10 or 11 will be switched from Income Support to the tougher Jobseeker's Allowance (JSA), which is paid at the same rate but requires them to attend fortnightly JobCentre interviews and show that they have applied for jobs or lose benefits.
Parents of children aged 12 or older were switched on to JSA last year, and the change will be extended to all single parents with children aged seven or over in October next year.
Plans to remove 300,000 lone parents from Income Support were announced in 2007 as part of a drive to achieve an 80 per cent employment rate, which some critics say is no longer a feasible goal in the light of rising joblessness caused by the recession.
The Department for Work and Pensions promised then that the increased obligations to look for work would be matched by "personalised help and support", with greater flexibility for JobCentre staff to respond to individual circumstances.
But Gingerbread today released a report suggesting that the lone parents who moved on to JSA a year ago did not get the support they needed.
Many did not get the meetings with a New Deal adviser to which they are entitled, said the charity. And others felt under pressure to find work and demoralised by repeated rejections.
In-depth interviews with 34 parents who switched to JSA in 2008 found widely varying experiences of job-hunting support, with some reporting only hurried fortnightly sign-on appointments and others complaining they had been offered inappropriate training courses.
Gingerbread chief executive Fiona Weir said: "The extra obligations are there but the support is woefully inadequate. Real, tailored help for single parent jobseekers must be built into the system from day one of a claim, otherwise it starts to look very much like a one-sided deal.
"From today, thousands more single parents with older children will go through Jobcentre Plus doors and on to JSA. They need a system that recognises their parenting role and that builds rather than erodes their self-confidence and their skills for work."
Ms Cooper said: "Already 80 per cent of all lone parents are either working or would like to work. And we know it's much better for families if parents can work. That's why we are changing the rules for parents with older children in school to help them find work.
"But parents also need extra support and welfare reforms must be family-friendly too. That's why we're increasing employment support through schools and children's centres as well as through the New Deal for Lone Parents.
"It's essential that everyone gets the personal help and advice they need on things like child care and training.
"Many parents also want to work part-time so they can pick their kids up from school or make sure they do their homework. So we're making it easier for parents to look for jobs that fit with school hours - both through regulations and developing changes to JobCentres too."
According to Government figures, the proportion of lone parents who go back to work before their youngest child reaches 10 has been rising steadily over the past decade to about 60 per cent.
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