Aim: Improving participation of children with disabilities is a priority; however, the participation construct lacks clarity. This systematic review investigated how researchers defined ‘participation’ and the language used in participation intervention research. Method: Nine health and education databases were searched for intervention studies of children with disabilities that included a participation outcome. Quantitative data were extracted using a customized form, and participation text data were extracted verbatim. Themes were derived using a thematic coding approach. These participation themes were applied to the outcome measures used in the included studies to compare participation language with the methods used to quantify participation changes. Results: Of the 2257 articles retrieved, 25 were included in this review. Five participation themes and nine subthemes were developed. Two themes, attendance and involvement, were directly related to the participation construct. Three additional themes described related concepts: preferences, activity competence, and sense of self. Interpretation: Attendance and involvement seem to describe the essence of the participation concept. The related themes may provide important avenues to enhance participation outcomes. This review highlighted the need for researchers to define the construct under investigation clearly and select measures carefully, as measurement choice is the mechanism through which the concept is operationalized in research.