He doesn't do that immediately, though. After dinner the four Apprentices go to the practical arena and Ruby tries to explain his magic intuitions to the other three. When he wonders aloud whether an Instructor wouldn't be better at this, Brelyna explains that while they might, Instructors of the College take a very hands off approach and mostly don't go into that much depth to teach students individual things; magic is a very broad subject, and it would be infeasible to teach everything one knows especially when the areas of interest of individual mages are very unlikely to perfectly overlap.
Plus, of course, as Ruby himself observed, a lot of it requires individual development. Magic, being an expression of the soul, has many indelible aspects that need to be worked out by each mage on their own.