This study aimed to describe 1-year changes in students' vocabulary in written narratives. Secondary aims included examination of accuracy and the relationship between lexical diversity and achievement. Participants included 749 students in first through eighth grades. Within-subjects 1-year change in diversity, productivity, and accuracy was examined across time points by grades. Findings indicated there was significant change in lexical diversity in early elementary grades with decreases in the proportion of spelling errors. There was significant change in the proportion of different words to total words in upper grades. Students' lexical diversity was moderately related to performance on standardized measures of achievement. Findings support the use of lexical measures as a tool to examine and describe written language growth.