Objectives and Background Scoring systems in Emergency Departments (EDs) are rarely validated. This study aimed to examine the Paediatric Observation Priority Score (POPS), a method of quantifying patient acuity, in EDs in the United Kingdom, and determine baseline performance characteristics. Methods POPS was implemented in 4 EDs for children (ages of 0 to 16) with participants grouped into 3 categories: discharged from ED, discharged but with return within 7 days, and admitted for less or more than 24 hours. Results 3323 participants with POPS scores ranging from 0 to 11 (mean = 2.33) were included. The proportion of each POPS score varied between sites with approximately 10–20% being POPS 0 and 12–25% POPS greater than 4. Odds ratio of readmission with POPS 5–9 against 0–4 was 2.05 (CI 1.20 to 3.52). POPS 0–4 showed no significant difference (p = 0.93) in relation to admission/discharge rates between sites with a significant difference found (p < 0.01) for POPS > 5. Conclusion It is feasible to implement POPS into EDs with similar performance characteristics to the original site of development. There is now evidence to support a wider health service evaluation to refine and improve the performance of POPS.