Average C-unit lengths in the discourse of African American children from low-income, urban homes.

This investigation reports average length of communication units (C-units) in words and in morphemes for 95 4- to 6 1/2-year-old African American boys and girls from lower-income homes in metropolitan Detroit. Mean C-units increased across the age span of this sample, and kindergartners produced significantly longer C-units than preschoolers. The syntactic complexity of the children's language samples correlated positively with increases in C-unit length, and regression analyses revealed that syntactic complexity was the best predictor of mean C-unit length. Children with longer average C-unit lengths produced greater frequencies of all types of syntactic complexity. Their language samples were distinguished from children with shorter mean C-unit lengths by clauses linked with coordinate and subordinate conjunctions. The findings indicate that average C-unit length will be useful as a quantitative index of linguistic growth in research designs focusing on young school-age African American children living in poverty.