The Basque version of the MacArthur-Bates Communicative Development Inventory (BCDI-1) can be used to evaluate 8–15-month-old children’s receptive and expressive verbal skills, as well as nonverbal gesture production. This paper reports on data of 1002 children of an extended age range obtained with the BCDI-1 as a proxy measure of Basque children’s communicative competence up to 24 months. Statistical analyses revealed a large effect of age on four BCDI-1 scales: phrases understood, production of gestures, receptive vocabulary, and expressive vocabulary, while sex, amount of exposure, educational level, and birth order showed small or no effect. The strong effect of age as well as the high between-scale correlations confirmed the advantage of using the BCDI-1 instrument for the extended age range.
