Roger Brown described Five Stages of Language Development based on the Mean Length of Utterance (MLU)
Roger W. Brown, as a result of his extensive research on children's language in 1973, described five stages of development based on the mean length of the their utterances (MLU).
He found that the linguistic complexity of language unfolded fairly predictably as each stage was attained. In fact the MLU was a better predictor of language development than age.
This is covered very well in the course text (and in most major books on Language Development) but we will review them briefly here.
While Brown did not assign ages to the five Stages, others have noted the most typical age range for each.
In Stage 1, the MLU ranges between 1.0 and 2.0 morphemes. Children's ages range from one to just over two years (26 mos.) Free morphemes are used exclusively.