In fragile X syndrome (FXS), social communication was a primary area of difficulties, and there were currently no acceptable outcome evaluation techniques. In order to evaluate future therapy trials, appropriate outcome metrics for FXS were recognized as a critical topic of scientific focus. The Brief Observation of Social Communication Change-Minimally Verbal (BOSCC-MV), a robust psychometric outcome measure created for autism spectrum disorder, holds promise as an outcome tool to determine social communication improvement in FXS patients. In this multi-site trial, researchers used central coders to test the BOSCC-suitability MV’s for FXS. Around 18 barely verbal men were aged 3–12 years were enrolled and tested over 2 days, with 7 participants returning 6 months later for a third examination. With standard clinical measures such as the Autism Diagnostic and Observation Schedule-2, Vineland 3, Social Responsiveness Scale, and the Aberrant Behavior Checklist, researchers looked at test-retest reliability, inter-rater reliability, convergent and divergent validity. The inter-rater and test-retest reliability of the BOSCC-MV in FXS were comparable to prior trials in idiopathic ASD. Autism Diagnostic Observation Schedule-2 and Vineland-3 both had high convergent validity. BOSCC-MV and unrelated measures were shown to have divergent validity. The BOSCC-MV shows promise as an FXS social communication outcome measure, indicating that it should be evaluated on a larger scale.