Published investigations of normative ages of speech sound acquisition vary in the kind of speech sample on which they are based and in the methods used. Review of norms based on elicited single-word responses shows that the methods used can influence the resulting ages of acquisition for specific speech sounds. Review of the investigations which sample children's spontaneous speech indicates that these data have characteristics that make them difficult to use as norms. Desirable characteristics of normative investigations of speech sound acquisition are proposed.

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