While there are many different frameworks seeking to identify what benefits young people might derive from participation in informal STEM (Science, Technology, Engineering and Mathematics) learning (ISL), this paper argues that the sector would benefit from an approach that foregrounds equity and social justice outcomes. We propose a new model for reflecting on equitable youth outcomes from ISL that identifies five key areas: (1) Grounded fun; (2) STEM capital; (3) STEM trajectories; (4) STEM identity work; and (5) Agency+. The model is applied to empirical data (interviews, observations and youth portfolios) collected over one year in four UK-based ISL settings with 33 young people (aged 11-14), largely from communities that are traditionally under-represented in STEM. Analysis considers the extent to which participating youth experienced equitable outcomes, or not, in relation to the five areas. The paper concludes with a discussion of implications for ISL and how the model might support ongoing efforts to reimagine ISL as vehicle for social justice.