The aim of the study was to evaluate children's and adolescents' understanding of items from self-report measures. Cognitive interviews were conducted as part of a larger study on pain and fatigue in children with disabilities. A list of guiding questions was used to encourage participants to talk about words or concepts in the scale that they found difficult. The sample included 32 children and adolescents with physical disabilities. Participants had difficulty with words such as intense, severe, and anxiety. They had more difficulty with abstract ideas, such as average, than they did with more concrete ideas, such as naming a recreational or social activity. Because poor outcome measurement hinders symptom evaluation, findings support the need to put greater emphasis on the child perspective when developing and using self-report measures. Suggestions for increasing accuracy of these measures are offered for clinicians and researchers.