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To evaluate the effect of 15° forward (FW) seat inclination and foot-support in children with cerebral palsy (CP) on postural adjustments during reaching. Observational study repeated-measures design; step two of two-step-project. Laboratory unit within University Hospital and two special education schools. 19 children (ten unilateral spastic CP (US-CP); nine bilateral spastic CP (BS-CP); Gross Motor Function Classification System levels I-III; 6–12 years old). Participants were able to take part for one one-hour session. Reaching while sitting in four seating conditions (FW or horizontal seat; with or without foot-support) applied in randomized order. Simultaneously, surface electromyography (EMG) of neck, trunk and arm muscles and kinematics of head and reaching arm (step one of two-step-project) were recorded. Primary outcome parameters were the ability to modulate EMG-amplitudes at baseline and during reaching (phasic muscle activity). Other EMG-parameters were direction-specificity (1st control level), and 2nd level of control parameters: recruitment order, and anticipatory postural activity. Motor behaviour measures: ability to modulate EMG-amplitudes to kinematic characteristics of reaching and head stability. Only foot-support was associated with increased tonic background EMG-amplitudes and decreased phasic EMG-amplitudes of the trunk extensors in children with US-CP and BS-CP (mixed-models analyses; p-values <0.01). The foot-support effect was also associated with better kinematics of reaching (Spearman's Rho; p-values <0.01). In terms of postural adjustments during forward reaching, foot-support enhanced the children's capacity to modulate trunk extensor activity, which was associated with improved reaching quality. FW-tilting did not affect postural muscle activity. • FW seat inclination does not affect postural EMG of reaching children with CP. • Foot-support in seated children with CP increases tonic trunk extensor activity regardless of CP type or seat inclination. • Increased tonic trunk extensor activity was associated with improved kinematics of reaching. [ABSTRACT FROM AUTHOR]