Research on the writing of students with intellectual developmental disorder (IDD) stresses the large variation in the quality and content of writing these students produce. This study investigates in detail the processes and temporal aspects of text production of nine Swedish upper-secondary students with mild IDD. The students wrote 27 narratives that were computer keystroke logged. The analysis of their keystroke-logs showed (1) that writing fluency was lower than in other special needs writer populations, (2) considerable variation in composition behaviour; and (3) that revision was mainly focused on deleting and editing typos, and spelling. The findings highlight the importance of instructional individualisation and compensation in writing instruction in special needs schools. These are necessary elements for students to be able to engage to the best of their abilities in text production, regardless of degree of their disability, comorbidity and motoric challenges.