The present study aimed to test the reliability and validity of the Person Centred and Experiential Psychotherapy Scale–Young Person version (PCEPS-YP). This is a newly developed and adapted 9-item scale which aims to measure counsellor competences in, and adherence to, person-centred practice, when working with adolescents. Counselling practice was assessed for 19 counsellors by randomly selecting 20-min audio segments from 142 recorded counselling sessions. Audio material was independently rated by eight raters using the PCEPS-YP to produce an average adherence rating per counsellor. Scale reliability was assessed via interrater reliability and internal consistency testing. Convergent validity was tested using ratings from the observer-rated Barrett-Leonard Relationship Inventory (BLRI Obs 40), and the scale was subjected to exploratory factor analysis. Results showed a high degree of internal consistency within raters (α = 0.95), marginally acceptable reliability across grouped raters (α = 0.58) and weaker reliability between pairs of raters (α = 0.50). Exploratory factor analysis revealed one strong factor for the scale with no subscales. Small-to-moderate correlations existed between the PCEPS-YP and the BLRI subscales and mean total score (rs = .12 to .40). Our findings suggest that the PCEPS-YP has potential as an effective, reliable and valid tool for assessing competence and adherence in person-centred practice with young people, both for research and for clinical purposes. However, training procedures need to be established that can enhance interrater reliability, and more evidence of convergent validity is needed.