In this single-subject study, we evaluated the effects of an intervention using a modified version of the Self-Regulated Strategy Development (SRSD) approach on the story composition skills and the use of mental state language in three writers with autism spectrum conditions (ASC). Interestingly, the intervention was not found to be effective in increasing the number of words, sentences and advanced words for all participants, while only two participants used more story elements and improved the holistic quality of their compositions. Nevertheless, all participants used more mental state terms, spent more time for story planning, transferred their new skills to different writing tasks and maintained them 4 weeks post-intervention. These findings demonstrate the effectiveness of the extended version of the SRSD approach on the use of mental state language in the writings of children with ASC.