Looked after children have frequently experienced complex developmental trauma manifesting as behavioural, cognitive and emotional challenges and difficulties in forming secure relational attachments to caregivers. Nurturing Attachments training was developed specifically to support carers who are parenting such children. The present study reports on a mixed-methods evaluation of this programme, focusing particularly on its impact on carer self-efficacy and behavioural manifestations of Reactive Attachment Disorder (RAD) which are common among looked after children, even if they are not formally diagnosed. Ten foster carers completed measures of self-efficacy and RAD before and after the training. A significant increase in carer self-efficacy was found but there was no overall change in levels of children's RAD-related behaviour. Semi-structured interviews were undertaken to explore the reasons for this. They revealed three key themes: reflection on then and now; knowledge and understanding; and contact with birth parents. These demonstrated how, after training, foster carers were able to reflect on changes in their own behaviours and draw on new knowledge and understanding. However, contact with biological parents remained challenging and some children seemed to show increased RAD-type behaviours associated with this. Results are discussed in terms of implications for training foster carers.