OBJECTIVE: Although there are several validated upper-extremity measures in young children with cerebral palsy, none of these primarily assess the capacity to carry out actions and tasks with the more-affected arm. To address this need, we developed the Pediatric Arm Function Test (PAFT), which involves the behavioral observation of how children use their more-affected arm during structured play in a laboratory or clinic. This article evaluates the reliability and validity of the PAFT Functional Ability scale. DESIGN: In study 1, a total of 20 children between 2 and 8 yrs old with a wide range of upper-extremity hemiparesis caused by cerebral palsy completed the PAFT on two occasions separated by 3 wks. In study 2, a total of 41 children between 2 and 6 yrs old with similar characteristics completed the PAFT and received a grade reflecting the severity of more-affected arm motor impairment. RESULTS: In study 1, the PAFT test-retest reliability correlation coefficient was 0.74. In study 2, convergent validity was supported by a strong inverse correlation (r = -0.6, P < 0.001) between the PAFT scores and the grade of impairment. CONCLUSIONS: The PAFT Functional Ability scale is a reliable and valid measure of more-affected arm motor capacity in children between 2 and 6 yrs old with cerebral palsy. It can be used to measure upper-extremity neurorehabilitation outcome. Copyright © 2012 by Lippincott Williams & Wilkins.