This internal rapid evidence review brought together findings from 15 existing evidence reviews of interventions to promote the success of girls and women in Computer Science (CS) and Science, Technology, Engineering and Maths (STEM). An overarching finding was a lack of both secondary and undergraduate-level counterfactual evaluations. Most of the conclusions of this paper are drawn from studies that took a qualitative approach or used pre- and post-test-only surveys. Most studies measured intermediate, self-reported outcomes just after the intervention, such as girls' interests or intentions, rather than uptake or achievement. None of the identified reviews explicitly reported on the involvement of non-binary people in interventions promoting the uptake of and achievement in CS or STEM. The included reviews did not identify experimental or quasiexperimental studies targeting girls' involvement in CS from the UK, and most of the findings presented below come from the USA. However, review findings were supplemented with results from recent UK-based research efforts such as the Gender Balance in Computing research programme. Overall, this context made it challenging to conclude what would offer the best return on investment, particularly at the undergraduate level.