I have twins too, Kent test next year, one will sit (he wants to at the moment) the other won't (he doesn't want to at the moment :) ) they are in the same sets, mainly, one is dyslexic, the other is being investigated for autism, I think they will take it well, I was 1 of only 3 in my class to fail in the days when everyone took it, the school I went to fitted me well.
that said I am buggered wth my two not doing it/failing as the in our town, three Grammars, two church (Catholic and C of E) 2 left...one closing next year, due to failing...so only one choice left, and massively over subscribed.
On failing, I remember the day at work a couple of years ago, when my admin's daughter passed her Kent test, I knew this was a bright child, Mum could not afford tuition so off her daughters own back, and we all late 30's early 40's talking about it, I was shocked to find me the manager, was the only one who failed, Admin, fitness adviser, nurses, doctors (Okay not them), technicians had all, every last jack of them passed!