From my eight years'
experience as a tutor, I can also say that for the most part
private tuition is unnecessary. In all those eight years probably
only one student I had truly benefited from tuition, and that was
only because she was hardworking and diligent. All she needed was
someone to guide her along.
For my 11 years experience as a tutor, having tried out many
varying styles of tutoring, I guess you are referring primarily to
home 1 to 1 tuition.
My main experience from home 1 to 1 tuition, is that it is
mostly unnecessary and a waste of parent's money. The money may be
good for tutors, seriously good, but it does not benefit the
student as much as small group tuition. In home 1 to 1 tuition, it
eventually boils down to answering homework for the student, much
more than actually coaching.
With small group tuition, there are a variety of things which I
can do and implement to help boost the students understanding. From
simple things such as showing educational video clips, doing simple
experiments, to leading class discussion, daring the students to
speak up and ask questions in class (something they need in
university anyway), to finally time trials, etc. Imagine going to a
home 1 to 1 tuition, and needing to bring all the equipment
necessary for these educational "supplements".
Other benefits of small group tuition includes listening to
questions posed by other students, and answers by the tutor, all
these apart from students making friends and sharing resources from
different schools with one another. I like it most when my tuition
group is actively asking questions to clear doubts, and every
student in the group get exposed to questions they may not have
thought of themselves. It's very beneficial to all the students, as
well as to me the tutor, who over time has grasp the most common
pitfalls of students, and compiled them into a book.
Example...

Certainly, there are instances
where 1 to 1 tuition are more beneficial. But for the majority, I
don't think so.
1 to 1 tuition makes the most money for the tutor but it is
questionable if it helps the student, really large group tuition
makes the most money for tuition centre but is most likely unable
to help most students.
I truly think small group tuition helps the majority of students
the most.