Objective: To evaluate the reproducibility, including reliability and agreement, of the Kids Balance Evaluation Systems Test (Kids-BESTest) and the short form of Kids-BESTest (Kids-Mini-BESTest) for measuring postural control in school-aged children with cerebral palsy. Design: Psychometric study of intrarater, interrater, and test-retest reliability and agreement. Setting: Clinical laboratory and home. Participants: Convenience sample of children (N=18) aged 8 to 17 years with ambulant cerebral palsy (CP) (Gross Motor Function Classification System I-II) with spastic or ataxic motor type. Intervention: Not applicable. Main Outcome Measures: Postural control was assessed using the Kids-BESTest and the Kids-Mini-BESTest. An experienced physiotherapist assessed all children in real time and the testing session was videotaped. The same physiotherapist viewed and scored the video twice, at least 2 weeks apart, to assess intrarater reproducibility. Another experienced physiotherapist scored the same video to determine interrater reproducibility. Thirteen children returned for a repeat assessment with the first physiotherapist within 6 weeks and their test-retest performance was rated in real time and with video. Results: Excellent reliability was observed for both the Kids-BESTest (intraclass correlation coefficient [ICC] 0.96-0.99) and Kids-Mini-BESTest (ICC 0.79-0.98). The smallest detectable change was good to excellent for all Kids-BESTest agreement analyses (5%-9%), but poor to good for Kids-Mini-BESTest analyses (9%-16%). Conclusion: The Kids-BESTest shows an excellent ability to discriminate postural control abilities of school-aged children with CP and it has a low smallest detectable change, suitable for use as a preintervention and postintervention outcome measure. Although the Kids-Mini-BESTest is 5 to 10 minutes shorter to administer, it has poorer reproducibility and focuses only on falls-related balance, which excludes 2 domains of postural control.