Claire, I found this on the TES community forum. Does it help?
“value added” is a term used to judge how good a school is doing compared to other schools with the same kind of intake. e.g. the local grammar school might get a higher percentage of A*-C grades but it is probably more selective in the kind of students it accepts than the local state funded comp. Value Added takes into consideration not only a child’s ability, but also their postcode, whether they are male or female (girls are expected to get higher grades than boys!), their ethnic origin, when their birthday is (students with September birthdays are expected to get higher grades than those with summer birthdays. Have a look at your bottom set students most of them will have June , July or August birthdays!). Each of these criteria is given a number (it’s a bit like handicapping in horse racing) and is added to the points already given for each GCSE, or equivalent, grade. The total number given to each student is based on their best eight GCSE grades, so if they don’t take eight GCSE exams you are pretty much on to a loser straight away. This of course is the reason why your SLT want all the children to study BTEC and GNVQ courses as they can achieve 4 equivalent GCSE A grades in the time it takes them to do some work and achieve one C in MFL. Any clearer?
Boadicea's Chariot 