To develop positive learning environments, it is important that supporting mental health and wellbeing is a priority. Whole-school programmes are considered an effective way of developing provision in schools; however, poor implementation can limit the impact of such programmes, and there is a lack of clarity about the key factors affecting the implementation of whole-school approaches. This small-scale study explored the implementation of a whole-school mental health and wellbeing programme, called Emotionally Friendly Settings (EFS). It aimed to consider the factors that facilitate and also act as a barrier to the effective implementation of whole-school wellbeing programmes. Individual semi-structured interviews were carried out with one member of staff in five settings: three primary schools, one secondary school, and one specialist setting. The sample included schools which reported the programme to have low impact, medium impact and high impact. Thematic analysis identified themes and sub-themes. Authentic versus tokenistic implementation was highlighted as a key factor influencing the impact of EFS. Linked to this were leadership; attitude to the programme; engagement; support; and programme characteristics. Findings are discussed in relation to existing implementation research, and implications for practice and areas for further research are highlighted together with the limitations of this study.