Purpose: Previous studies investigating the effectiveness of exergame balance-training (using video-games) in children with cerebral palsy (CP) yielded inconsistent results that could be related to underpowered studies. Therefore, in this multicenter intervention study, we investigated whether exergaming improves balance clinically in spastic CP. Materials and methods: In total, 35 children with unilateral or bilateral spastic CP (GMFCS-level I–II) were included (age-range: 7–16 years); 16 at VUMC (trial: NTR6034), 19 at UHG (trial: NCT03219112). All participants received care as usual. The intervention group (n = 24) additionally performed exergame-training; 6–8 weeks home-based X-box One Kinect training focused on balance. Balance performance was assessed with the pediatric balance scale (PBS) and two subscales of the Bruininks–Oseretsky Test of Motor Proficiency-2nd edition (“balance” [BOTbal] and “running speed and agility” [BOTrsa]). Mixed model ANOVAs with between and within factors were used to test differences between and within groups. Results: On group level, no post-intervention differences were found between the intervention and control group (PBS: p = 0.248, η_p² = 0.040; BOTbal: p = 0.374, η_p² = 0.024; BOTrsa: p = 0.841, η_p² = 0.001). Distribution of CP-symptoms (unilateral versus bilateral) did not affect training (PBS: p = 0.373, η_p² = 0.036; BOTbal: p = 0.127, η_p² = 0.103; BOTrsa: p = 0.474, η_p² = 0.024). Children with low baseline balance performance (based on PBS) in the intervention group showed improvements in balance performance after training (PBS: p = 0.003, η_p² = 0.304; BOTbal: p = 0.008, η_p² = 0.258), whereas children with high baseline balance performance did not. Conclusions: This exergame-training resulted in balance improvements for the current population of CP that had a low baseline function.IMPLICATIONS FOR REHABILITATION Exergame-training (training using video-games) shows mixed results in children with cerebral palsy (CP). Children with spastic CP (GMFCS level I–II) with a high baseline balance-level did not show functional balance improvements after this home-based exergame-training, suggesting that these children should not be enrolled in this type of exergame-training protocol. Children with spastic CP (GMFCS level I–II) with a low baseline balance-level showed clinically relevant functional balance improvements after this home-based exergame-training, suggesting that these children can benefit from enrolment in this type of exergame-training protocol to improve their balance. The distribution of CP-symptoms did not affect the effectiveness of this balance exergame-training in children with spastic CP with GMFCS-level I and II.