Like I said, it all depends on what the writer goes on to say next. Here, I am assuming that the general sense is 'the acadmeies per se' — though I might have expected the source text word order to have been "In themselves, academies in the UK are not improving education..." or even "Academies in the UK in themselves are not improving education...". What cocnerns me about the word order as given is that it leaves open the possibility that the writer meant "...are not improving education within their own establishments" I feel this is unlikely, however, since to start with, I'd have hoped the writer might have said 'within themselves' (which would have been unambiguous); and also, it would seem a slightly odd statement to make.

So my guess is that what th writer was trying to say was that the mere fact of the presence of these academies isn't actually doing anything directly to improve education, but that they are in some way having an indirect effect on eduction.

Hard to tell which way to take it without more context — is the writer critical of or seeking to praise the academies themselves, or the decision to set them up?

--------------------------------------------------
Note added at 19 minutes (2015-02-01 10:06:46 GMT)
--------------------------------------------------

Apologies for the typo: it should of course be 'existence' in the singular!

--------------------------------------------------
Note added at 30 minutes (2015-02-01 10:17:37 GMT)
--------------------------------------------------

Ok, here is a longer quote that helps put the statement into context:

" NUT: Call for transparency

“This is an utterly damning report which shows that children’s education is being run in an incoherent and unaccountable fashion,” said Kevin Courtney, Deputy General Secretary of the National Union of Teachers (NUT), affiliated to Education International (EI).

“Free schools and academies are clearly not improving education in themselves,” he added. “This has been obvious from the start, yet the Coalition Government has persisted in championing them as the solution to education in England.” "

So although it remains non-explicit, I think it is in fact criticizing the lack of results from the setting-up of these academies.

Au Royaume-Uni, même les établissements privés n'apportent aucun bénéfice dans l'enseignement.
Dans le contexte, "in themselves" peut être transposé par "même".

Bonsoir, une idée.

Academies in the UK are not improving education in themselves
les écoles privées au Royaume-Uni n'améliorent pas l'enseignement par elles-mêmes
==> c.à.d. "toutes seules".

Salutations.