This study explores the changes in Computer Science (CS) students' self-efficacy between entering study and the end of first year of university. It aims to give course leaders insights into the everyday challenges that affect students' academic achievement and persistence into second year. The paper begins by proposing that the way CS is taught, the gender imbalance on CS courses, and the experience of the key transitional year into university might influence CS students' non-continuation. It adopts an academic buoyancy conceptualisation of resilience. Acknowledging the scarcity of instruments covering CS students' transition to university, the development of a new 20-item questionnaire is described, based on CS students' own contributions of the challenges they faced during first year. The instrument is administered twice in one session to the same cohort. Analysis of paired responses indicates a loss of confidence to overcome challenges in most aspects, particularly staying motivated to study.