Digital tools are an integral part of most writing communities across the globe, enhancing the criticality of gaining a comprehensive understanding of both paper and computer-based writing acquisition and development. The relationships between transcription skills and children's paper-based writing performance are well documented. Less is known about the relationships between transcription skills and children's computer-based writing performance. In this study, we examined the unique contributions of transcription skills (i.e., handwriting automaticity, keyboarding automaticity and spelling) in predicting Grade 2 students (N = 544) paper-based and computer-based writing performance (i.e., compositional quality and productivity) after controlling for other student-level factors (i.e., gender, word reading, reading comprehension, and attitudes towards writing) and classroom-level factors (i.e., amount of time teaching handwriting, keyboarding, and spelling). Multilevel modelling showed that, compared to handwriting automaticity, spelling skills accounted for a larger percentage of unique variance in predicting paper-based compositional quality; handwriting automaticity accounted for a larger percentage of unique variance in explaining paper-based compositional productivity. Findings further showed that keyboarding automaticity accounted for a larger percentage of unique variance in students' computer-based compositional quality and productivity when compared to spelling. Gender and word reading skills were also found to be uniquely related to students' writing performance across modalities. These findings underscore the need for educators to address and nurture the automaticity of inscription and spelling skills to enhance students' compositional quality and productivity, whether in traditional paper-based or computer-based text composing.