Aim Optimal motor skill acquisition frequently requires augmented feedback or knowledge of results (KR). However, the effect of functional declines on the benefits of KR remains to be determined. The objective of this research was to examine how cognitive and motor deficits of older adults influence the use of KR for motor skill learning. Methods A total of 57 older adults (mean 73.1 years; SD 4.2) received both cognitive and eye–hand coordination assessments, whereas 55 young controls (mean 25.8 years; SD 3.8) took only the eye–hand coordination test. All young and older participants learned a time‐constrained arm movement through KR in three pre‐KR and post‐KR intervals. Results In the subsequent no‐KR skill retests, absolute and variable time errors were not significantly reduced for the older learners who had KR during skill practice, especially for those with cognitive and motor dysfunctions. The finding suggests that KR results in no measureable improvement for older adults with cognitive and motor functional deficiencies. More importantly, for the older adults, longer post‐KR intervals showed greater detrimental effects on feedback‐based motor learning than shorter pauses after KR delivery. Discussion The findings support the hypothesis about the effects of cognitive and motor deficits on KR in motor skill learning of older adults. The dynamics of cognitive and motor aging, external feedback and internal control mechanisms collectively explain the deterioration in the sensory‐motor learning of older adults. The theoretical implications and practical relevance of functional aging for motor skill learning are discussed. Geriatr Gerontol Int 2013; ●●: ●●–●●.