Little published research studies examined the relationship between cohesion and writing quality of L2 children's narrative texts using scientific tools such as Automatic Analysis of Text Cohesion (TAACO) and Coh-Metrix. To fill the research gap, this study investigates the development of cohesive devices and writing quality of 59 ESL grade four students over one semester using TAACO and Coh-Metrix. The corpus for the current study contained 177 narrative texts. Results show that L2 grade four children's use of cohesive devices and the quality of writing has improved over one semester. Low proficiency group of students tends to use more cohesive devices than high proficiency group. Multi-dimensional assessment of writing quality shows that referential cohesive devices would be positive predictors of complexity by length and subordination. The study has contributed new knowledge in the field of second language writing in terms of research, theory, and pedagogy.