Background: The COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) is an international initiative that offers standardized and validated tools to guide the appraisal of patient-reported outcome measures in healthcare. Aims: To explore the use of a new set of tools from the COSMIN to appraise studies on one outcome measure available to speech and language therapists (SLTs). Methods & Procedures: We used the COSMIN tools to appraise seven studies and a user manual that reported the measurement properties of the Focus on the Outcomes of Children Under Six (FOCUS), a validated measure of pre-schoolers' communicative participation that is used in various contexts around the world. Outcomes & Results: Using COSMIN guidelines, the FOCUS was categorized as a 'category A' tool because there was a sufficient level of evidence to support its content validity and internal consistency. According to the COSMIN guidelines, this means that the FOCUS can be recommended for use. The quality of evidence supporting measurement properties of the FOCUS received a rating of 'moderate', meaning users can have moderate confidence in its measurement properties. Since these ratings from the COSMIN tools may be unclear to users of the FOCUS, we have provided more specific recommendations. Conclusions & Implications: The COSMIN tools offer detailed standards to support the appraisal of outcome measures available to SLTs. However, several limitations were observed, and recommendations to support the application of the COSMIN tools are provided.