This qualitative case study explored the writing assessment practices of upper elementary ELA teachers and factors that influenced their decision making when assessing student writing. Effective assessment practices are important because these practices can aid teachers in identifying student needs, designing tailored writing instruction, and monitoring student progress. This study included 5 teacher participants from 3rd to 5th grade. Participants were viewed as 1 case bound by their grade band and employment in a district focused on teaching and assessing writing. Data was collected through semi-structured interviews, a think aloud task, a review of assessment artifacts and the researcher’s reflective journal. Analysis was completed following a five-phase model. Findings included: (1) teachers’ efficacy of assessing student writing is influenced by support received, (2) strengthening teachers’ assessment practices requires personalized, ongoing PD, (3) context influences teachers’ decision making when assessing student writing, and (4) teachers have varying levels of knowledge of formatively assessing student writing. These findings suggest implications for state administrators, district and school administrators, classroom teachers, curriculum leaders, and university programs.