Research in the study of students' writing concludes that vocabulary use is a key variable in determining the holistic quality of the writing. In the present study, 77 writing samples from a mixed group of Grade 3 children were analyzed for features of linguistic diversity using public domain vocabulary-profiling software. The writing was also evaluated holistically on a trait-based rubric. Data analysis identified the salient features of linguistic diversity correlating to quality standards of writing; the key is "lexical stretch" or use of low-frequency and "off-list known" words. Implications for assessment include the potential to identify children in need of vocabulary enrichment at an early stage in the educational trajectory and to track their evolving vocabulary growth in the shape of their lexical profile over time.