I've never tried to actually test the difference between learning a skill through tutoring or learning it through practice, but my impression is that Sims learn a lot faster when being tutored. In the Flowers Waiting for Grim story, my instructors have done a lot of skill tutoring with Sims that have no skills or skill-related traits, and it surprises me how fast it is. One of the skills that takes a lot of time to gain through practice is painting, and it definitely increases faster through tutoring. Of course, all the tutoring in that game is at lower skill levels. I imagine it would take longer at the higher levels.