Challenges in Assessing Writing - Aspect of Writing - Literacy continuum

I found assessing student writing and putting them into clusters very challenging as a specific student is put in a higher cluster by another Marker and creates an anomaly in the Clusters students are put in by Markers.  I find students' writing is related to a specific subject/content/knowledge of spelling strategies and hence they are grouped in different clusters. Alternatively, it demonstrates the student's ablility to extend his writing and thus justify grouping him in a higher cluster.

The Literacy continuum has to be an ongoing process throughout the year.