BACKGROUND AND PURPOSE: The aims of this study were to develop a clinical 
assessment scale to measure functional ability in ambulant boys with Duchenne 
muscular dystrophy and to determine the reliability of the scale in multiple 
centres in the UK.
METHODS: Focus groups and workshops were held with experienced paediatric 
neuromuscular physiotherapists to determine scale content. A manual was prepared 
with accompanying videos, and training sessions were conducted. A total of 17 
physiotherapists from participating centres used the videos to determine 
inter-rater reliability. Five determined the intra-rater reliability.
RESULTS: Strength of agreement for these groups based on total subject scores 
was very good (0.95 and ≥ 0.93 for consistency and absolute agreement, 
respectively). Test-retest ability was high, with perfect agreement between 
occasions for all but two items of the scale.
CONCLUSIONS: Our study indicates that the North Star Ambulatory Assessment is 
practical and reliable. It takes only 10 minutes to perform and incorporates 
both universally used timed tests as well as levels of activities, which allow 
assessment of high-functioning boys with Duchenne muscular dystrophy.