Purpose: To scale language milestones in a group of 527 children to provide an instrument for screening language development.
Procedure: The questionnaire regarding these milestones was completed by parental report. It was evaluated whether the scaled milestones satisfied the assumptions of the Mokken item response model.
Results: The scalability of the final scale of 14 milestones was strong (H = .95), its reliability was high (p = .96), and it satisfied the assumptions of the Mokken model.
Conclusions: A single, unidimensional scale of diverse milestones was developed. It tops lexical, syntactic, and phonological skills, as well as both receptive and expressive language skills, and is well suited for mapping progress in language ability.