Writing is one of the most complex cognitive skills students develop, yet most K–12 students receive limited real-time feedback on their writing as they work. TrueMark is an AI-enhanced writing platform that provides students with a personalized Socratic copilot for in-the-moment guidance while giving teachers tools to monitor student progress, track AI usage, detect plagiarism, and grade with AI assistance. In this research, conducted independently by Quantily, LLC and funded by an IES SBIR Phase IB grant, a mixed-methods pilot study examined the usability, feasibility, and perceived effectiveness of TrueMark's personalized AI copilot and core platform features across multiple schools serving grades 7–9, as well as platform-based skill growth estimates across five writing domains. Teachers generally found the platform's AI copilot and academic integrity features to be useful additions to their writing instruction and identified opportunities to further develop the dashboard and automated scoring features. Student-level findings indicate a correlational relationship between sustained platform use and growth in platform-based skill estimates. This research will be valuable to education leaders, curriculum coordinators, ELA teachers, and school administrators considering AI-enhanced tools for writing instruction.