I'll semi-agree with Kate. A few years ago, we implemented tutoring by the course TAs for students who were really struggling, usually because of inadequate preparation or miserable math skills. We found we had to put in a "miss two sessions and you lose your slot" policy, as struggling students also often blew off the tutoring session, partly I suspect because it was free.
Tutoring can work really well for a student who needs to see the material again, and who comes to the session having looked over her notes and with questions. There, I've seen 30-60 minutes with the tutor each week changing a low C into a mid-range B (or even in one extreme case, a student who had failed twice ending up with an A!) It can be nearly useless for a student who comes with nothing, hasn't looked at anything, and isn't even sure where to start. Of course, I'm also talking about college students, where "taking responsibility for your own learning" is actually appropriate!
I'm very interested in this question - thanks so much for taking the time to comment.
Based entirely in personal experience, I've come to the conclusion that tutoring is 'bad' -- i.e. it's a bad model for learning (& teaching). It's like buying a lemon and then taking it to the shop a whole lot.
However, the question still remains: if you've got a 'lemon,' in the form of an ineffective school or curriculum, then what?
How well can tutoring work when there's no other option?