Critical reflective practice is a foundation of socially just pedagogy. This paper focuses on the informal STEM (science, technology, engineering, and maths) learning sector, where there is an acute shortage of support for critical reflective practice despite long-standing, entrenched issues of inequity. We analyse how practitioners used a new reflective tool, the Equity Compass, co-developed by researchers and practitioners through a five-year partnership. We report on multimodal qualitative data (interviews, ethnographic observations, group discussions, partner site visits, and workshops) from 12 practitioners in four settings in the UK: a community zoo, regional science centre, digital arts centre and an initiative supporting girls and non-binary young people into STEM. We discuss how using the Equity Compass: (i) increased and deepened practitioners' knowledge and understanding of equity issues; (ii) supported personal and institutional critical reflection, helping practitioners move beyond 'gut instinct' to interrogate their own positionality, ask new questions, and critically evaluate the effectiveness of attempts at inclusive practice; and (iii) fostered more intentional equitable planning and practice, such as participatory approaches that shared authority with learners and introduced more inclusive forms of representation. We conclude by discussing the challenges, limitations, and implications for supporting critical reflective practice among educators.