The title is misleading. This isn't an AI tutor so much as a practice quiz platform with an AI autograder.

> constructed-response questions (CRQ) are graded by Claude Sonnet 4.6 against instructor-defined, question-specific rubric criteria

> Crucially, LLMs make it feasible to grade formative CRQ against rubric criteria at scale, a capability that appears pedagogically significant rather than merely convenient.

They specifically call out that the "RAG chat assistant" part of Phosphor (the platform) wasn't used much.

I commend the effort here, but I don't think these results are particularly noteworthy. The conclusion is essentially that people who do practice quizzes will do better on exams.