This has been a rollercoaster week for independent schools.
Firstly, the Charity Commission reminded them they must demonstrate how they provide a public benefit, including to those who cannot afford their fees, if they are to retain charitable status.
Secondly, one of the most innovative and outspoken independent school head teachers, Dr Anthony Seldon from Wellington College, accused his own sector of remaining "entrenched in the 20th century".
Dr Seldon argued that it is "not right" for independent schools to "cream off" the brightest pupils and "the best teachers". He argued they should put something back into the state system through an involvement in academies, trust schools, or federations.
Few subjects generate as much heated debate as "independent" education; it tends to bring out tribal tendencies.
The arguments about public benefit are complex. They tend to get bogged down in hard-to-answer questions about the exact impact of independent schools on their state school neighbours.
Meanwhile, criticism of the independent sector's funding advantage is countered by the argument that parents who pay school fees pay twice for education: once through their taxes for a service they do not use and again through their contribution to independent schools.
Parents in the independent sector have certainly had to dig deeper. Over the past 20 years, fees have more than doubled even after allowing for inflation. Some of that money, of course, has gone to fund bursaries for students from low-income families.
But until now there has been very little hard evidence of the impact of independent schools on their state-funded counterparts.
Now, though, new research from economists at the London School of Economics has highlighted one measurable way in which state schools are losing a valuable resource, namely teachers, to the independent sector.
In their study of "Competition for Private and State School Teachers", the LSE economists argue that there is a "loss" to state schools, and an equivalent "bonus" to private schools, in the net flow of publicly-trained teachers into the private sector.
They have produced some interesting statistics. While the independent sector educates just over 7% of all pupils in England, it employs 14% of teachers.
The apparent mismatch is because of the much smaller class sizes in independent schools.
Interestingly, the class size difference - as measured by pupil-teacher ratios - has widened since the 1980s. The ratio is now 18:1 in the state sector compared with 9:1 in independent schools.
So, with fee income rising ahead of inflation, the independent schools have used this premium to recruit teachers at a faster rate than pupils.
They have also particularly recruited better-qualified and more experienced teachers, as well as those in shortage subjects, like maths and science.
Thus while the proportion of male state school teachers with a higher degree is 45.2%, in the private sector it is 55.6%. A similar gap is evident when comparing teachers with higher degrees in sciences, maths and engineering. The gap amongst female teachers is also evident, although less marked.
In 2006, independent schools recruited 1,125 teachers straight out of universities and training colleges.
In addition, they recruited 2,009 experienced teachers from state schools. The flow, of course, is not all one way, as some teachers move back into the state sector. But the net flow to the independent sector was 1,400 experienced teachers in 2006.
The report says this amounts to a "significant loss" on the state's investment in teacher training and that this transfer of experience teachers is a "substantial bonus" for the private sector.
State school 'damage'
Of course, parents paying school fees could argue that this means they are getting at least some small return for the taxes they pay on top of school fees.
When this research was presented at a Nuffield Foundation seminar last week it drew a furious response from the head teacher of a well-known independent school. He said he had, in his many years of headship, received only five applications from teachers at state schools and had never appointed any.
What I found surprising about this response was not only the defensive anger but also the sense that this sort of research was an attack on private schools.
Rejecting the charge of "poaching" teachers, this head teacher insisted that the independent sector was attracting much-needed, high quality graduates who might otherwise not have entered teaching at all.
Pointing to the independent sector's academic achievements in science subjects, he added: "For the first time in our history, this country cannot do without the products of the independent sector - yet our sector gets no credit for that".
How much of the excellent academic performance in the private sector is down to the recruitment of the best-qualified and most experienced teachers from the state?
He does indeed have a good point about the achievement in science. But what most struck me was the contrast between his defensiveness and the views of Dr Seldon, who argued that the independent sector should do more to help state schools, precisely because of its privileged position.
In fact, much of the LSE research was music to the ears of the independent sector. It underlined the smaller classes, the better working conditions for teachers, and the long-term benefits, in terms of future earnings, for its pupils.
It also did what research tends to do: it raised yet more questions. How much of the excellent academic performance in the private sector is down to the recruitment of the best-qualified and most experienced teachers from the state?
And, to what extent - if at all - does this outflow of teachers damage state schools?
Some of these questions may be impossible to answer. But it does seem that within the independent sector there are two very different responses to scrutiny: one is that the independent sector should be left alone to do its own thing and the other says, on the contrary, it should do more to share its successful recipe with state schools.
What the LSE research seems to show is that, whatever your views of the rights or wrongs of private education, you cannot say it has no impact on state schools.
As to the exact nature of that impact, I leave that to your tribal tendencies if you have any.