Ecological momentary assessment (EMA) was used to further validate the real-world predictability of the Family Assessment Device (FAD) among low income, racial and ethnic minority, urban families of children (7–12 years) with asthma. Caregivers completed self-report measures at baseline, as well as daily assessments of family functioning for 2 weeks through EMA delivered via smartphone. Concurrent validity was established with measures of caregiver perceived stress and positive and negative affect at baseline. Better family functioning at baseline was associated with EMA reports of families getting along better and of being better able to balance multiple family needs, including child asthma management. Consistent with previous literature, findings suggest the FAD is an ecologically valid measure for use with urban families of children with asthma. Researchers and clinicians may be confident that assessments of family functioning in research and clinical settings are predictive of what may be happening in the family’s everyday life.