OBJECTIVE: Language development is important for children's success in life. Therefore, language is monitored by child health care professionals and parents, but a uniform set of milestones in language development is lacking. Our aim was to identify a set of clear and distinctive milestones that empirically reflect language development in children aged 1 to 6 years of age.
METHODS: We obtained a community-based sample of 1381 parents reporting on milestones derived from clinical signs and currently used language screening instruments. We used nonparametric Item Response Theory analysis to identify milestones belonging to one unidimensional scale.
RESULTS: Twenty-six milestones were excellently scalable (item H coefficients 0.62-0.90) and formed a strong scale (total H coefficient 0.83). The final set of identified milestones covered vocabulary, grammar, and communication, with an item ordering that holds for all children.
CONCLUSIONS: This unidimensional set of 26 clear and distinctive milestones reflects language development in young children and can be used as an instrument to monitor language development.