Due to the limitations of standardized neurodevelopmental testing in individuals with AS, obtaining an accurate picture of the neurodevelopment profile is challenging. Standardized tests, like the Bayley Score of Infant and Toddler Development-3 (BSID-3), are not adapted to children with special needs, and this results in those individuals being underestimated on a test score. It is recommended that individuals with intellectual disability be evaluated with measures that are better suited for their developmental age. The BSID-3 developers have made allowances within the manual for making accommodations for children with special needs, however, in order to be useful for research studies, these accommodations need to be standardized. While these adaptations have been developed in other languages including the BSID-3 Special needs version, this is available in Dutch and not English. This study, in collaboration with the ABOM, was designed to modify the English version of the BSID-3 to create a special needs edition, and reduce dependence on expressive language and fine motor skills in order to more accurately assess the neurodevelopment of AS individuals.