Mean length of utterance

Mean length of utterance

Mean Length of Utterance (or MLU) is a measure of linguistic productivity in children. It is traditionally calculated by collecting 100 utterances spoken by a child and dividing the number of morphemes by the number of utterances. A higher MLU is taken to indicate a higher level of language proficiency.

A study by Bishop and Adams (1990) suggests that MLU at age 4.5 is a good predictor of reading ability at age 8. Nonetheless MLU is considered controversial, and should not be used as the only diagnostic measure of language proficiency in children.


  • Bishop, D. V. M., & Adams, C. (1990). A prospective study of the relationship between specific language impairment, phonological disorders and reading retardation. Journal of Child Psychology and Psychiatry, 31, 1027–1050.

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