Building AI applications for large scale assessment requires substantial efforts not just from data science, but also psychometrics, hand-scoring, item development, UI/UX, and machine learning engineering to ensure products can support trustworthy AI (e.g., NIST AI Risk Management Framework) in ways that are also cost effective. This presentation will discuss the key elements and steps our team took when designing and building a writing feedback tool called “Write On with Cambi!” that walks students through reviewing their essay using structured feedback and highlighting organizational and grammatical elements in the essay to emphasize areas for review. The presentation will cover the how the overall purpose for product drove the design, structure, and human labeling of the annotations, the AI modeling using fine-tuned lightweight open source models, the evaluation of the human and AI annotations including bias evaluations, as well as the mapping of elements to structured feedback, the UI/UX, and finally efficacy studies conducted with students and teachers.