This study tests a handwriting model for children and youth with Autism Spectrum Disorder (ASD) that displays the relationships between handwriting process and product characteristics, and the predictors of these characteristics. Structural Equation Modelling was used to test the model for children and youth with ASD (n = 50) and typically developing peers (n = 50), ages 10 to 15, for a copying and freestyle handwriting task. Findings suggest a generic handwriting model applying to both groups and both handwriting tasks. Unique effects for children and youth with ASD were identified for: (1) high interdependence of handwriting process characteristics; (2) longer pen stroke in air leading to better legibility; and (3) lower scores for executive functions leading to lower scores for legibility.