Abstract: As of July 2017, we identified four trials with 192 participants that met the review inclusion criteria. Participating parents were mostly mothers (seven fathers were included in two studies), and children's ages ranged from one month to six years and five months. One study was conducted in Australia, one in Canada, one in the Netherlands, and one in the USA. Each studied a different intervention and considered different outcomes. Three interventions were delivered at home, and one in a community venue (e.g. a church). Interventions varied in duration from seven weeks to 12 months. They included a range of practical childcare skills, home safety and developing parents' ability to respond sensitively to their children. Parents in the comparison groups included in the review received treatment as usual and most of these received the index intervention after the study was complete. One study was funded by the Ontario Mental Health Foundation and the Ontario Ministry of Community and Social Services Research Grants Program; one by the Alabama Development Disabilities Council; one by the Best Practice Parenting Education Initiative of the Commonwealth Department of Family and Community Services and the New South Wales Aging and Disability Department; and one by ZonMw, The Netherlands Organisation for Health Research and Development. It was not possible for us to conduct a meta-analysis. The GRADE quality assessment varied from very low to moderate across the studies. Primary outcomes No study reported on the 'attainment of specific parenting skill targets'. 'Safe home practices' and 'understanding of child health': one study (30 parents, very low-quality evidence) reported some improvements in parents' knowledge of life-threatening emergencies, ability to recognise dangers, and identify precautions, in favour of the intervention group. It also found limited, very low-quality evidence that parent training improved parents' ability to understand child health, implement precautions, use medicines safely, recognise child illness and symptoms, and seek medical advice (i.e. visit the doctor). Another study (22 mothers, very low-quality evidence) reported improved attainment of skills related to childcare and safety, in favour of the intervention group. Secondary outcomes 'Parent-child interaction': one study (40 mothers, very low-quality evidence) reported improved maternal-child interaction following parent training at 12 months follow-up. Another study (83 mothers, 2 fathers, moderate-quality evidence) reported that inclusion in the intervention group led to a steeper decline in parenting stress related to the child compared to the control group. 'Parents' retention of child': one study (22 participants; very low-quality evidence) reported that before joining the programme nine of 11 (82%) families with a previous child had had the child removed from their care by child protection authorities due to maternal maltreatment, compared with only four of 22 (19%) families after participating in the programme (only one of these four mothers had also had a previous child removed). No study reported data on: 'return to independent care of child' or 'lifting of child-related court order'. There is some very low-quality evidence that some parents, mainly mothers, with intellectual disabilities are able to provide adequate parenting if they are given appropriate training and support to learn the parenting skills they need. However, there are few studies exploring how interventions might work, for whom and in what circumstances. In particular, there have been few studies that include fathers with intellectual disabilities, or that explore the views of parents themselves. There is a need for larger RCTs of parenting interventions, with longer follow-up, before conclusions can be drawn about the effectiveness of parent training for this group of parents.

Plain-language summary: The four RCTs were conducted in Australia, Canada, the Netherlands and USA, and involved 192 parents. Each studied a different intervention and considered different outcomes. All but seven of the participating parents were mothers. Children's ages ranged from one month to six years and five months. Three interventions were delivered at home, and one in a community venue (e.g. a church). Interventions varied in duration from seven weeks to 12 months. They included a range of practical childcare skills, home safety and developing parents' ability to respond sensitively to their children. Parents in the control groups all received treatment as usual. Each study was sponsored by different funders. One study was funded by the Ontario Mental Health Foundation and the Ontario Ministry of Community and Social Services Research Grants Program. Another was funded by the Alabama Development Disabilities Council. A third was funded by the Best Practice Parenting Education Initiative of the Commonwealth Department of Family and Community Services and the New South Wales Aging and Disability Department. The fourth study was funded by ZonMw, The Netherlands Organisation for Health Research and Development. Compared to those parents without parent training, the studies reported some improvements in parents in the intervention group. One study reported improvement in safe home practices, recognition of child illness and safe use of medicines, in favour of the intervention group. Another study reported improvements in childcare and safety, also in favour of the intervention group; and a third study found that parents who had attended parent training reported less child-related parenting stress compared to the control group. A fourth study reported improvement in mother-child interaction in the intervention group compared with the control group. No study reported that interventions caused harm. The quality of the evidence ranged from very low to moderate. There is some low-quality evidence that parent training interventions for parents with intellectual disabilities may support their parenting. It may also help to establish good parent-child relations. However, given the low quality of the evidence, the results should be interpreted with caution. Better-quality research is needed to evaluate the effectiveness of parent training interventions for parents with intellectual disabilities. These studies should include fathers and follow-up participants over a longer time period.