Objective The aim of this study was to establish the construct validity of the Focus on the Outcomes of Communication Under Six (FOCUS©). This measure is reflective of concepts in the International Classification of Functioning Disability and Health – Children and Youth framework. It was developed to capture ‘real‐world’ changes (e.g. communicative participation) in preschoolers' communication following speech‐language intervention. Method A pre–post design was used. Fifty‐two parents of 3‐ to 6‐year‐old preschoolers attending speech‐language therapy were included as participants. Speech‐language therapists provided individual and/or group intervention to preschoolers. Intervention targeted: articulation/phonology, voice/resonance, expressive/receptive language, play, and use of augmentative devices. Construct validity for communicative participation was assessed using pre‐intervention and post‐intervention parent interviews using the FOCUS© and the communication and socialization domains of the Vineland Adaptive Behavior Scales‐II (VABS‐II). Results Significant associations were found between the FOCUS©, measuring communicative participation, and the VABS‐II domains for: (i) pre‐intervention scores in communication (r = 0.53, P < 0.001; 95% CI 0.30–0.70) and socialization (r = 0.67, P < 0.001; 95% CI 0.48–0.80); (ii) change scores over‐time in communication (r = 0.45, P < 0.001; 95% CI 0.201–0.65) and socialization (r = 0.39, P = 0.002; 95% CI 0.13–0.60); and (iii) scores at post‐intervention for communication (r = 0.53, P < 0.001; 95% CI 0.30–0.70) and for socialization (r = 0.37, P = 0.003; 95% CI 0.11–0.50). Conclusions The study provided evidence on construct validity of the FOCUS© for evaluating real‐world changes in communication. We believe that the FOCUS© is a useful measure of communicative participation.