BACKGROUND: 'Situation Awareness For Everyone' (SAFE) was a 3-year project which aimed to improve situation awareness in clinical teams in order to detect potential deterioration and other potential risks to children on hospital wards. The key intervention was the 'huddle', a structured case management discussion which is central to facilitating situation awareness. This study aimed to develop an observational assessment tool to assess the team processes occurring during huddles, including the effectiveness of the huddle. METHODS: A cross-sectional observational design was used to psychometrically develop the 'Huddle Observation Tool' (HOT) over three phases using standardised psychometric methodology. Huddles were observed across four NHS paediatric wards participating in SAFE by five researchers; two wards within specialist children hospitals and two within district general hospitals, with location, number of beds and length of stay considered to make the sample as heterogeneous as possible. Inter-rater reliability was calculated using the weighted kappa and intraclass correlation coefficient. RESULTS: Inter-rater reliability was acceptable for the collaborative culture (weighted kappa=0.32, 95% CI 0.17 to 0.42), environment items (weighted kappa=0.78, 95% CI 0.52 to 1) and total score (intraclass correlation coefficient=0.87, 95% CI 0.68 to 0.95). It was lower for the structure and risk management items, suggesting that these were more variable in how observers rated them. However, agreement on the global score for huddles was acceptable. CONCLUSION: We developed an observational assessment tool to assess the team processes occurring during huddles, including the effectiveness of the huddle. Future research should examine whether observational evaluations of huddles are associated with other indicators of safety on clinical wards (eg, safety climate and incidents of patient harm), and whether scores on the HOT are associated with improved situation awareness and reductions in deterioration and adverse events in clinical settings, such as inpatient wards.