A government initiative to help the most disadvantaged families in England has made no "significant impact", a report suggests.
The Troubled Families Programme launched in 2012 at a cost of £448m, with £900m added as it was extended.
The National Institute of Economic and Social Research suggests it has had no measurable effect on school attendance, employment or behaviour.
But the government said families had seen "significant improvements".
Dame Louise Casey, who led the Troubled Families Team in the Communities and Local Government Department, will answer questions from the Commons Accounts Committee, which monitors government spending, on Wednesday.
The programme - set up by former Prime Minister David Cameron following the 2011 riots in English cities - was intended to turn around the lives of 120,000 of the most "troubled" families.
It focuses on areas affected by high levels of unemployment, truancy and anti-social behaviour.
To qualify for the scheme, families must have at least two of the following problems:
- Parents or children are involved in crime or anti-social behaviour
- Children have not been attending school regularly
- Children need other types of extra help
- Adults are unemployed or "at risk of financial exclusion" or young people are at risk of worklessness
- There is domestic violence and abuse
- Parents or children have a range of health problems
The scheme stresses "targeted interventions", with families getting dedicated workers who help with everyday tasks. They teach, for example, better household management and control of children's behaviour. They also have to show "persistence", visiting the families often.
The government pays councils up to £4,000 to work with each of the hardest-to-help families, on a payment-by-results basis.
This includes cutting children's truancy and school exclusion rates and offending rates, as well as at least one adult getting into work.
In 2015 the scheme was extended for a further five years, to cover another 400,000 families at a potential estimated cost of £900m.
Perfect case study
The government has previously said the lives of tens of thousands of families have been "turned around".
But the National Institute of Economic and Social Research (NIESR) found no consistent, measurable evidence that the scheme had improved the lives of families it aimed to help.
Using data from a quarter of the families taking part in the first stage, it found "a very small number of positive or negative results".
"Across a wide range of outcomes, covering the key objectives of the Troubled Families Programme - employment, benefit receipt, school attendance, safeguarding and child welfare - we were unable to find consistent evidence that the programme had any significant or systematic impact," the report stated.
Jonathan Portes, one of the authors, called the programme a "perfect case study" of how the manipulation and misrepresentation of statistics by civil servants and politicians meant bad policy-making and money-wasting.
Dominic Cummings, who was special adviser to former Education Secretary Michael Gove during the early years of the programme, published a series of tweets criticising Mr Cameron over the troubled families project. He called its handling a "farce" and claimed it had not been "thought through", adding that when Mr Gove's team had questioned the scheme, it had been labelled "crazy".
In August, BBC Two's Newsnight reported a leaked version of the NIESR's report, saying its publication had been "suppressed" - claims the government denied.
The prime minister's official spokeswoman said: "The work that's been done by the government to look at the impact of the programme shows that these families have seen significant improvements in their lives.
"We've seen improved school attendance, youth crime down, anti-social behaviour down and in more than 18,000 cases an adult holding down a job for three months or more, which is an improvement on the situation before."
She added that the government was "absolutely committed to continuing to help this group of people", adding: "Of course we should look at the evidence to see how it's working and see how things could be done differently, to learn from it and see if there's more we can do to help these people."