This research investigates the overarching question of ‘How do we know if young people in a positive youth development (PYD) programme have developed?’ The specific focus is on a particular PYD self-assessment measurement tool which was developed in 2009 as a means of supporting YWCA Auckland to assess individuals’ growth and development through the period they participate in the organisation’s PYD programme. The aim of this research is to determine the success of the tool in supporting the programme’s objectives for positive development by critically examining the experience of using of the self-assessment tool by YWCA staff and programme participants. A qualitative methodology approach based on interpretivism is used. Research findings are formed from interpretation of the research participants’ voices from semi structured interviews. The findings of this research provide a basis for recommendations to enhance the use and outcomes of the tool in the future.