ObjectivesTo retrospectively evaluate the comparative effect of 2 wheelchair seating systems, Custom-Contoured Wheelchair Seating (CCS) and Modular Wheelchair Seating (MWS), on scoliosis progression in children with neuromuscular and neurologic disorders and to determine any predictors for scoliosis progression. DesignLongitudinal, retrospective cohort study. SettingA national health service regional posture and mobility service. ParticipantsNonambulant pediatric wheelchair users with neuromuscular and neurologic disorders (N=75; 36 men, 39 women; mean age at seating intervention, 10.50±3.97y) issued CCS and MWS by the South Wales Posture and Mobility Service from 2012-2022. InterventionsTwo specialized wheelchair seating systems, CCS and MWS. Main Outcome MeasuresA generalized least squares model was used to estimate the effect of seat type on Cobb angle over time. ResultsOf the 75 participants enrolled, 51% had cerebral palsy. Fifty were issued CCS and 25 were issued MWS. Baseline Cobb angle was 32.9±18.9° for the MWS group and 48.0±31.0° for the CCS group. The generalized least squares model demonstrated that time since seating intervention (χ2=122, P<.0001), seating type (χ2=52.5, P<.0001), and baseline scoliosis severity (χ2=41.6, P<.0001) were predictive of scoliosis progression. Condition was not a strong predictor (χ2=9.96, P =.0069), and sex (χ2=5.67, P=.13) and age at intervention (χ2=4.47, P=.35) were not predictive. Estimated contrasts of medical condition with seat type over time demonstrated smaller differences between MWS and CCS over time. Predicted scoliosis velocity was found to attenuate with use of CCS over time compared with MWS, although scoliosis deteriorated regardless of intervention. ConclusionsOur findings showed pediatric wheelchair users with neurologic and neuromuscular disorders prescribed CCS showed greater mitigation of scoliosis progression over time compared with those issued MWS.