The Evaluation of Social Interaction (ESI; Fisher & Griswold, 2008) assesses a person's performance of social interaction skills in the natural context with typical social partners during any area of occupation. We used Rasch analysis of 175 observations of 128 people, ages 4–73, to examine internal scale validity, the items’ skill hierarchy and intended purpose, and the ESI's ability to differentiate between people with and without disabilities. The ESI demonstrated validity for 24 of 27 skills and six intended purposes, with a hierarchy of performance. Of the observations, 95.3% demonstrated goodness of fit to the Rasch model, indicating person response validity. People without a disability demonstrated significantly higher social skills performance than those with a known disability (t = 4.468, df = 83 p = .000). The ESI has the potential to provide a quantitative assessment of social interaction performance in the natural context of a person's desired occupation and may be useful for intervention planning and outcome measurement.