Background: It is widely agreed that more needs to be done to improve participation in science, technology, engineering and mathematics (STEM). Despite considerable investment in interventions, it has been difficult to discern their effectiveness and/or impact on participation. Purpose: This paper discusses findings from a six-week pilot STEM careers intervention that was designed and overseen by a teacher from one London girls' school. We reflect on the challenges for those attempting such interventions and the problems associated with evaluating them. Sample: Data were collected from Year 9 students (girls aged 13-14 years) at the school. Design and methods: Pre- and post-intervention surveys of 68 students, classroom observations of intervention activities, three post-intervention discussion groups (five or six girls per group) and a post-intervention interview with the lead teacher were conducted. Results: Although the intervention did not significantly change students' aspirations or views of science, it did appear to have a positive effect on broadening students' understanding of the range of jobs that science can lead to or be useful for. Conclusions: Student aspirations may be extremely resistant to change and intervention, but students' understanding of "where science can lead" may be more amenable to intervention. Implications are discussed, including the need to promote the message that science is useful for careers in and beyond science, at degree and technical levels.