I wish I could write two separate reviews for Babylon idiomas: One for the teaching staff and one for the rest. The teachers were way above average (of what I have experienced in many other language schools). I stayed for four weeks, so I had a lot of different teacher. Of couse, some of them were not very motivated, but others were the best I have ever had. I am studying to become a teacher, so I know good teaching when I see it.
But the organisation of the school did not convince me at all. I complained in my first week that the level of my group was too low, but the headmistress refused to change my group (as I was in the highest level already). The only solution would have been private lessons (just one hour per day instead of four), which I was given one week when there was no C1 class. Then I had to attend the normal lessons again, which was quite frankly often a waste of time, as it was just a repetition of what I already knew. I was told that the administration does not allow group lessons to be changed for private lessons, so they just tell you that you are in the right group.
I would therefore not recommend the school for people who already have a good knowledge of Spanish.
And what bothered me even more is the fact that the school tries to rip you off with their additional offers, like accomodation. For my 4 weeks I would have had to paid 1000 Euros, which is simply ridiculous considering the fact that you can find a decent room for just 350 Euro (which I did). And the host families just receive about half of what you pay, the school gets the rest. The same applies to salsa classes,... So I would urge you just to book lessons and nothing else. You will save lots of money!