The dynamic nature of intellectual disability (ID) and its many comorbidities necessitate repeated screening and functional diagnosis. However, the existing scales are lengthy and expensive and cannot be implemented at all levels of ID. During phase one of this study (September 2019–September 2020), the functional screening tool (FST-ID) was validated for adults with ID and then used as a clinical tool to collect data for 76 participants from their direct service providers (DSP). Their age ranged from 21 to 71 years (mean = 37.63, SD ± 14.61), and they were diagnosed with severe/profound (N = 16) and moderate (N = 29), and mild (N = 31) levels of ID. The scale was found to hold high psychometric values. During phase two (September 2020–June 2022), the scale was found to be reliable as a continuous, clinical on-going screening tool, enabling the screening of functional and environmental changes experienced by adults with ID during acute times of the pandemic and regular times alike. All 76 adults experienced changes at the senior’s daycare center mostly. The new scale may also help in the future to determine whether those changes only relate to post COVID-19 symptoms or other comorbidities as well.