Mutismo seletivo is characterised by consistent selectivity in speaking, such that a child demonstrates adequate language competence in specific social situations, typically at home, but consistently fails to speak in others, typically at school. The disturbance lasts for at least one month, is not limited to the first month of school, and is of sufficient severity to interfere com educational achievement or com social communication. Failure to speak is not due to a lack of knowledge of, or comfort com, the spoken language required in the social situation (e.g. a different language spoken at school than at home).