BackgroundFunctional hand splinting is a common therapeutic intervention for children with neurological conditions. The aim of this study was to investigate the effectiveness of the Cognitive Orientation to daily Occupational Performance (CO-OP) approach over and above conventional functional hand splinting, and in combination with splinting, for children with cerebral palsy or brain injury.MethodsA multisite, assessor-blinded, parallel, randomized controlled trial was conducted in Australia. Participants (n = 45) were randomly allocated to one of three groups; (1) splint only (n = 15); (2) CO-OP only (n = 15); (3) CO-OP + splint (n = 15). Inclusion: age 4–15 years; diagnosis of cerebral palsy or brain injury; Manual Ability Classification System I–IV; hand function goals; sufficient language, cognitive and behavioral ability. Primary outcome measures were the Canadian Occupational Performance Measure (COPM) and Goal Attainment Scale (GAS). Treatment duration for all groups was 2 weeks. CO-OP was provided in a group format, 1 h per day for 10 consecutive weekdays, with parents actively involved in the group. Hand splints were wrist cock-up splints that were worn during task practice. Three individual goals were set and all participants were encouraged to complete a daily home program of practicing goals for 1 h. Analyses were conducted on an intention to treat basis.ResultsThe COPM showed that all three groups improved from baseline to immediately post-treatment. GAS showed a statistically significant difference immediately post-intervention between the splint only and CO-OP only groups p = 0.034), and the splint only and CO-OP + splint group (p = 0.047) favoring CO-OP after controlling for baseline.ConclusionsThe CO-OP Approach™ appeared to enhance goal achievement over and above a functional hand splint alone. There was no added benefit of using hand splints in conjunction with CO-OP, compared to CO-OP alone. Hand splints were not well tolerated in this population. Practice of functional goals, through CO-OP or practice at home, leads to goal achievement for children with cerebral palsy or brain injury.Trial registrationRegistered with the Australian New Zealand Clinical Trials Registry (ACTRN12613000690752) on 24/06/2013.Electronic supplementary materialThe online version of this article (10.1186/s12887-018-1213-9) contains supplementary material, which is available to authorized users.