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This is a plain English summary of an original research article. The views expressed are those of the author(s) and reviewer(s) at the time of publication.

Children from low-income families, or with an unemployed or single parent, benefitted as much as did economically advantaged groups from parental training. The Incredible Years programme worked better for children with more severe behaviour problems or a parent with depression.

This NIHR-funded review pooled individual-level data for pre-school and primary aged children with persistent disruptive behaviours. The 14 European trials, including eight studies in the UK, took place in diverse settings including schools, children’s centres and mental health clinics.

The Incredible Years parent training is widely funded in the UK by the NHS, local authorities and voluntary organisations. Parents gain skills to support their children at risk of or with behavioural problems. These findings show that the programme has the potential to improve outcomes for both advantaged and disadvantaged families similarly.

NICE already recommends evidence-based parenting programmes for children with conduct problems. Commissioners may need to provide additional resources for outreach to the most socially disadvantaged or disengaged families.

Why was this study needed?

In 2004, 7% of boys and 3% of girls aged five to 10 had a diagnosable conduct problem. Prevalence rates were higher amongst children from socially deprived households. These persistent disruptive childhood behaviours can lead to substance abuse, poor education, and involvement in crime in adolescence and adulthood. Annual costs from age 10 to 28 have been estimated as £351 million for additional education, and £1,360 million for the criminal justice system.

Several UK trials have shown positive benefits from the Incredible Years intervention for children with behavioural problems. Training, supervision and implementation checks ensure fidelity to the developers’ manual in this licensed parenting programme.

The research to date has given conflicting findings on whether disadvantaged families, who might most, need help, and those with more severe problems derive greater or less benefit. This review aimed to use a sufficiently large dataset to test whether effectiveness differs according to family and child characteristics and whether there is potential for reducing inequalities in outcomes or at least not making them worse as some programmes might.

What did this study do?

This systematic review analysed data from 14 of the 15 European randomised controlled trials completed by 2015. Reviewers asked study authors to provide individual-level participant data for combining into one large dataset of 1,800 families.

Trials compared the Incredible Years Basic Programme (12 to 14 weekly sessions) to a waiting list control (ten trials), minimal intervention or usual care. Children were on average aged five years. Nine trials included only children with a clinical level of disruptive behaviours. About a third of practitioners were certified in Incredible Years.

Unavoidably, parents and practitioners were aware of their allocation to treatment groups; the reviewers assessed trials as having a low risk of bias. The reviewers had to make assumptions to combine data from trials using different measures.

Behaviours were rated on the 36-item Eyberg Child Behavior Inventory Intensity scale (ECBI-I), in which higher numbers indicate a higher level of disruptive behaviours.

What did it find?

  • At two months following programme completion, the intervention had led to a moderate reduction in parent-rated disruptive behaviour, compared to a waiting list control, minimal intervention or usual care. Unadjusted pooled standardised mean difference 0.46, range 0.01 to 1.25 in individual trials. A difference of over 0.3 is often considered important on such a measure.
  • Having a low income did not change how much the programme reduced behavioural problems (effect modification index [EMI] 1.9 points on the ECBI-I, 95% CI -4.8 to 8.6 points; 13 trials, 1,614 families). Neither did whether they were unemployed nor a single parent.
  • There was no difference in effectiveness according to ethnicity, nor for the age of the child.
  • The programme’s effect was greater for children with worse baseline behaviours (EMI -4.3 points, 95% CI -7.9 to -0.7 points; 13 trials, 1,622 families). It was also more effective for children with a depressed parent (EMI -4.8 points, 95% CI -8.4 to -1.1 points; 11 trials, 1,395 families).
  • The programme cost £2,414 per person on average (range £1,733 to £2,586 as offered across five UK trials, 2014 prices, excluding set-up costs), with an average offer of 13 sessions. Potential savings across health, justice and education over 20 years ranged from £1,000 to £8,400 per child and probably offset the cost of the intervention.

What does current guidance say on this issue?

The NICE guideline (updated 2017) recommends group parent training for children aged three to 11 with or at high risk of developing an oppositional defiant disorder or conduct disorder or in contact with the criminal justice system due to antisocial behaviour.

Individual programmes can be delivered to families with severe and complex problems or when parents are unable to participate in a group.

NICE specified that parent training should follow a manual, be based on social learning, and enable parents to rehearse scenarios and receive feedback to improve parenting skills.

What are the implications?

This group parenting programme appears to be an effective method of early intervention which works equally across social groups. Commissioners may need to expand capacity with accredited programme facilitators to meet families’ needs in disadvantaged areas. The cost of programmes and the extent to which this intervention might produce benefits for local budgets in other sectors, such as justice or education, will need to be considered.

Engaging and retaining socially disengaged and minority ethnic families may require proactive outreach and support through schools, GPs and trusted local voluntary organisations

Incredible Years is the only parenting programme assessed by the Early Intervention Foundation to have evidence of positive impacts across populations and settings from multiple high-quality evaluations.

Citation and Funding

Gardner F, Leijten P, Mann J, et al. Could scale-up of parenting programmes improve child disruptive behaviour and reduce social inequalities? Using individual participant data meta-analysis to establish for whom programmes are effective and cost-effective. Public Health Res. 2017;5(10).

This project was funded by the National Institute for Health Research Public Health Research Programme (project number 12/3070/04).



NICE. Antisocial behaviour and conduct disorders in children and young people:  recognition and management. CG 158. London: National Institute for Health and Care Excellence; 2013; updated 2017.

NICE. Antisocial behaviour and conduct disorders in children and young people. QS59. London: National Institute for Health and Care Excellence; 2014; updated 2017.

NICE. NICE support for commissioning for antisocial behaviour and conduct disorders in children and young people. London: National Institute for Health and Care Excellence; 2014.

Produced by the University of Southampton and Bazian on behalf of NIHR through the NIHR Dissemination Centre


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Challenging behaviours are normal from time to time in children’s development. Conduct problems are non-age-appropriate persistent disruptive behaviours. Oppositional defiant disorder (mainly under age 11) and conduct disorder (older children) are diagnosable conditions. It has been estimated that a further 10% of primary aged children have moderate behavioural problems, which may come to the attention of GPs or teachers. The Incredible Years parenting programme is based on a collaborative social learning model involving videos, role play and peer support. Parents are set goals for home practice and receive weekly telephone calls.  
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