This paper reports on an analysis of the assessment principles used in marking students' written texts in the UK. It considers the assessment advice offered markers with respect to two stories written by 14 year old students in the Key Stage 3 English test in England. The observations offered on the written texts are shown to be general and lacking in much understanding of the ways the texts work linguistically. Using the functional grammar, an attempt is made to explore aspects of the grammatical organization of the two texts, and hence to reveal why one text was deemed superior to the other.