By the time children are of preschool age their oral language development is complex and rich. This complexity makes assessment difficult. The only way to truly capture the full richness of children's langauge development is to tape their conversations as they speak and transcribe them word for word along with a detailed description of the context in which the language was used. The transcript can then be analyzed to detrmine the average length of sentences used, forms of langauge etc. However doing that would be too time consuming and impractical in most classrooms.