This paper reports the findings of a study of student writing that assessed the skill needs of a cohort of developmental writing students enrolled in a co-requisite composition course at a community college that is part of the City University of New York (CUNY). This credit-bearing course fulfills the first half of the required composition component at the college and includes additional instructional hours to support developmental writing students. A cohort of students who were enrolled in the course over three separate semesters (Fall 2020, Fall 2021, and Spring 2022) completed a diagnostic writing assessment, which asked students to compose an essay in response to a writing prompt. The assessments were graded with an analytic rubric to determine if any particular skill areas were most challenging for these students. Course pass rates were also compared to student performance on the diagnostic assessment to explore if overall skill level, entering the course with particular skills, and mastery of specific skills in the course might relate to course success. Findings indicated that while students exhibited developmental needs in a wide variety of skills, essay organization and development challenges were most common in the cohort and might complicate successful course completion. Recommendations include the following: the routine use of diagnostic skills assessment; the use of pedagogical approaches that are proven effective for students with developmental needs (e.g., scaffolding, strategies-based instruction, low-stakes writing assignments, essay models); and proactively connecting students with tutoring services.