children's language development follows a predictable sequence. However, there is a great deal of variation in the age at which children reach a given milestone. Furthermore, each child's development is usually characterized by gradual acquisition of particular abilities: thus "correct" use of English verbal inflection will emerge over a period of a year or more, starting from a stage where vebal inflections are always left out, and ending in a stage where they are nearly always used correctly.
There are also many different ways to characterize the developmental sequence. On the production side, one way to name the stages is as follows, focusing primarily on the unfolding of lexical and syntactic knowledge: