He's at the university level, but it's certainly a class accessible to sufficiently advanced high-schoolers: he's not what you'd call strict about grading so long as you show sufficient enthusiasm for the subject, and there is a certain amount of leeway built into the syllabus for him to spend time going off on philosophical tangents or getting distracted by telling stories about stuff he's seen and done. (Some students make a game of seeing if they can drag him off-topic - he's aware that they're playing him, but he lets it happen to some degree because he likes to tell stories.) So if Naoto wants, say, a kind of downtime class that will give her college-level science credits and also time to organize her notes from her other classes, she's quite welcome!