Background: ETAP-1 was created to evaluate the quality of services trajectory from families' perspective. The items of ETAP-1 were developed from previous studies on integrated care, existing quality assessments, and consultations with families and experts in evaluation and in autism spectrum disorder (ASD). Method: The questionnaire was completed by 200 parents of children aged 5 and under who were recently diagnosed with ASD or intellectual disability. Of these, 183 received diagnostic evaluation through a clinic specialized in ASD; the other 17 underwent diagnostic evaluation in hospital settings. Results: Factor analysis supported the a priori dimensions of quality and distinctions between experiences before and during diagnostic evaluation. The instrument had high internal consistency, convergent and discriminant validity with other measures and was sensitive to differences in service delivery models. Discussion: ETAP-1 is useful in organizing information on families' experiences throughout their services trajectories and according to a dynamic perspective.