Aim: Our aim was to develop an outcome measure, called Focus on the Outcomes of Communication Under Six (FOCUS), that captures real-world changes in preschool children's communication. Conceptually grounded in the World Health Organization International Classification of Functioning, Disability and Health framework, the FOCUS items were derived from observations of change provided by parents and clinicians after speech-language therapy. Method: Participating families (n = 165) were drawn from a convenience sample at partner institutions in Ontario, Newfoundland and Labrador, and Nova Scotia. All children had speech, language comprehension, and/or language production disorders and were receiving speech-language therapy. The age of the children ranged from 1 year 2 months to 5 years 6 months (mean = 3.8y; SD = 0.91y), and 119 children were male. Three test phases were completed. The measure was revised according to item analysis and parent/clinician feedback after phase 1 (n = 74) and phase 2 (n = 65). In phase 3 (n = 26), the Pediatric Quality of Life Inventory (PedsQL), a health-related quality of life measure, was added to establish construct validity. Results: In phase 1, item analysis revealed high internal consistency for both parents (Cronbach's alpha = 0.87) and clinicians (Cronbach alpha = 0.97). These values indicated redundancy, so 31 items were cut. Five items for young children were added. In phase 2, internal consistency remained high for both parents (Cronbach alpha = 0.98) and clinicians (Cronbach alpha = 0.83), indicating redundancy of items. Twenty-seven items were removed. In phase 3, parents and clinicians reliably scored the FOCUS in 10 minutes. They stated that it provided an accurate snapshot of the child's communication. Internal consistency for parents remained high (Cronbach alpha = 0.96). Children with higher FOCUS scores at the end of treatment had higher PedsQL total scores (r = 0.466, p = 0.029). Interpretation: The FOCUS is a usable measure of a child's ability to communicate and participate in his or her community. It demonstrates high internal consistency and construct validity. (Contains 2 figures.)