Ok, for those students who intend doing the test here is some information that may be very useful.
First of all, you should visit the Cambridge English webpage. There you will find a lot of useful information and lots of tips and sample tests for you to prepare.
To do so, please click on the following link: http://www.cambridgeenglish.org
You can also try to read this document which I downloaded from www.gave.min-edu.pt: Projeto Key for Schools Portugal.
And after you do pass the exam (which I am sure you will!) you get a certificate that will look like this: Key for Schools Certificate Sample.
Well then, prepare, do your best but, above all, relax and trust in yourself!