This study examined narrative and argumentative essays written over the course of a 4‐month semester by 37 students of English as a second language (ESL). The essays were analyzed for development over time and for genre differences. The goal of the study was to conceptually replicate previous studies on genre differences (e.g., Lu, 2011) and on short‐term linguistic development in the areas of syntactic complexity, accuracy, lexical complexity, and fluency (e.g., Connor‐Linton & Polio, ). In addition, the authors wanted to investigate whether native speakers exhibited similar genre differences in order to determine if the ESL students’ genre variations were developmental or related to functional differences between the genres. The results indicate strong genre differences in the area of linguistic complexity. There were limited changes over time on most measures and a notable lack of development in the area of accuracy. Parallel data from native speakers show genre variation on some but not as many of the measures. Although this study was motivated by research design concerns, it also has implications for theory (e.g., the source of genre differences) and pedagogy.