The purpose of language sample is to determine the level of the child's development. It is important to observe the stages of his/her development in relation to the "norm". Nonetheless, a sample transcript is not necessarily representative of the child's ability. Factors such as the child being too shy or too tired many contribute to inaccuracy of the transcript. It is possible that the child is capable of a lot more than he/she is demonstrating throughout the transcript. Furthermore, when evaluating the child's language development, syntactic, semantic, and pragmatic analysis are looked at.
Unik, Yelena, "Issues in Language Sample Analysis of Russian Speaking Children" (2006). Honors College Theses. Paper 30.