The aim of this study is the quantification of the effectiveness of a computer-assisted system to improve upper extremity function (Armeo Spring system) in hemiplegic children with Cerebral Palsy using clinical-functional scales and upper limb kinematics. Eight children with hemiplegia were evaluated by clinical examination (Quality of Upper Extremities Skills Test and Melbourne Assessment) and 3D movement analysis in a test involving the upper limb during a reaching task. They were assessed in two sessions: before the Armeo Spring treatment and at the end of the 4-weeks program. After Armeo Spring training the clinical scores improved significantly. Some significant improvements were present in terms of upper limb kinematics; in particular, the movement duration, the velocity of movement execution, the Average Jerk and Number of Unit Number improved significantly. Our results suggest that the proposed program can have positive effects on upper limb function in hemiplegic children.