Intellectual disability (ID) is assumed to be a dynamic phenomenon influenced by personal and environmental factors. During the 18 months of the coronavirus disease (COVID-19) pandemic, most day centers remained open for adults with ID who lived with their families (most of them with severe/profound [S/P] ID) but were closed to those who lived in group homes (with moderate and mild ID). Owing to the fewer participants in day centers, adults with S/P ID received more hours of therapy than before the pandemic. Using a functional screening tool, functional and environmental changes were mapped and discussed in team meetings. As expected, the pandemic caused environmental and personnel changes that affected all groups. The moderate (n = 29) and mild (n = 31) groups deteriorated over the 18 months of the study, especially the senior ones. However, the functional state of the S/P group (n = 16) improved. These results support the understanding that ID is truly dynamic throughout the lifespan. Functional improvements for S/P ID can occur during adulthood with intense and individually adapted interventions.