Background: The primary-secondary transition can negatively affect pupils' emotional and psychological adjustment. However, methods for assessing concerns regarding secondary school are limited. A reliable and valid measure of transition-related concerns would be useful both in evaluating and shaping the content and delivery of universal and targeted transition support programmes. Aims: To assess the validity of a quantitative self-report measure of school concerns as an assessment tool during the primary-secondary school transition. Sample: A UK sample of 147 Year 6 primary school pupils and 263 Year 7 secondary school pupils. Method: Self-reports of school concerns and school liking as well as self-reported and peer assessments on a range of psychological adjustment measures were collected. Results: The School Concerns Questionnaire (SCQ) showed good reliability at primary and secondary school. Secondary concerns reduced significantly post-transition. Three factors emerged from an exploratory factor analysis of the SCQ and the pattern of results was replicated for post-transition concerns. Pupils with higher school concerns at secondary school reported reduced liking of school and reduced trust and respect for teachers. The SCQ was associated with generalized anxiety and female gender both pre-and post-transition. Peer problems and depression were associated with pre- and post-transition concerns, respectively. Conclusions: The SCQ is a simple to complete, reliable, and valid tool for assessing primary-secondary transition concerns. It could serve a valuable role in the evaluation and development of universal and targeted school-based initiatives that aim to promote positive secondary transition.