The evaluation of YMHFA training implemented by London-wide practitioners within their respective settings showed this training to be significantly effective in delivering mental health provision within settings. This was evidenced by significant increases in practitioners' rating on beliefs on six evaluation belief constructs: (A) confidence in knowledge and awareness of mental health conditions, (B) administering MHFA ALGEE dialogic action plan to converse with young people about maintaining good mental health by asking, listening non-judgementally, giving reassurance and information, enabling seeking professional help and encouraging use of self-help strategies, (C) engaging in evidence-based practice, (D) developing young people's mental health literacy, (E) influencing whole setting collective efficacy of staff, parents and young people to help young people's mental health and seek help themselves if needed, and (F) influencing young people's self-efficacy to recognise their own mental health issues and knowing what self-help strategies and professional support to draw upon.