This study explores the writing performance of deaf high school students, focusing on narrative, argumentative, and argumentative-with-sources genres, and examining the role of expressive language proficiency and early language exposure. Using a descriptive research design, the writing samples of 75 students were scored for idea development, organization, style, sentence fluency, word choice, and conventions using automated scoring. Results revealed a range of low to mid performance, with the argumentative-with-sources writing scoring similarly to narrative writing and showing incremental growth across the grade levels. Early language exposure and proficiency in ASL or spoken English were linked to better writing outcomes, highlighting the importance of early and accessible language development. The results underscore the urgent need for linguistically responsive materials, reliable ASL assessments, and evidence-based instructional strategies for addressing the range of needs of deaf students. The study calls for further exploration of the patterns observed in students’ writing to design instruction that builds on strengths and addresses needs, enhancing academic success and societal participation for deaf learners.