With the emergence of generative artificial intelligence, dialogue systems like chatbots are redefining traditional concepts of authorship and impacting critical aspects of writing. In educational contexts, previous research has pointed out new opportunities associated with using chatbots for writing instruction and support. This study involved 108 students across 10 classes in Norwegian K-12 education, examining how they employed educational chatbots as a support tool in L1 writing assignments. Through an inductive, data-driven thematic analysis of 895 student prompts, five recurring patterns emerged: information requests, structural guidance, example requests, content creation, feedback on text, and follow-up clarification. Aggregated results show that information requests were the most common pattern, particularly among younger students, whereas content creation and feedback on text were more prevalent among secondary and upper secondary students. Illustrative examples from the conversations revealed that generative AI extensively produced content on student’s behalf, even when students primarily sought scaffolding. The study proposes that effective scaffolding of writing through educational chatbots requires not only refining students' prompting strategies but also enhancing system designs that better support pedagogical use of generative AI.