Brown described five stages of language development based on a child’s mean length of utterance (MLU).  His research demonstrated that MLU was a better predictor of what linguistic structures a child was able to use than was chronological age.  This research, which examined three children whom Brown dubbed Adam, Eve, and Sarah, was the ultimate explanation of language acquisition for years.  The complexity of Brown’s description has also, unfortunately, painted language acquisition as a complicated morass of agent+actions, entities+locatives, recurrences, and nominatives that quite frankly, has turned off many students (especially speech-language pathology students) from this entire area.  The structural analysis of language samples based on Brown’s language description is a staple of the SLP college experience often remembered with revulsion.  Despite this, the influence of this study can not be denied.  Neither can it’s untouched accuracy in describing the process of language development.

The best online description of Brown’s work is at Caroline Bowen’s speech therapy site.