Writing is an important skill for children's academic success, underlining the need for effective ESL writing instruction in the elementary classroom. However, there is a paucity of research on elementary ESL writing instruction in Canada. Specifically, we have little understanding about the pedagogical practices in this context. To fill this gap, this article reports on findings of a study that investigated (a) factors that influence teacher preparedness, and (b) challenges that teachers encounter in teaching ESL writing. Eight elementary teachers, each with at least three years of teaching experience, participated in the study. Data were collected from interviews and online surveys. Findings suggest that teacher preparedness was affected by four factors: (a) background knowledge of teaching ESL writing, (b) professional learning opportunities, (c) self-learning and experience as a teacher, and (d) collaboration, mentorship, and support for teachers. The challenges teachers encountered were grouped into five categories: (a) making sense of the writing curriculum, (b) finding relevant resources, (c) lack of time, (d) difficulty providing feedback, and (e) parental involvement at home. Drawing on these findings, the article discusses implications and recommendations for ESL writing instruction in the elementary classroom.