Warwickshire is the month before KE. You don't have to be within the 17 mile circle to take it. But you WILL have to be quite on the ball to register (the forms come out at the beginning of July and have to be back within a few days) and you won't get results until March (which is at least one step better than KE!). I put our daughter in for it last year as familiarisation. She would say it was helpful, I would say I doubt it made much (if any) difference. But I have too much on my plate at the moment to argue the point with the Foundation about being given her KE results so I can't say for certain. (By the way - if you do put your child in for Warks, bear in mind that the invigilator may engage him/her in small talk after the exam and ask about things like school choices which can be quite an awkward moment for them
There are imho a few things you have to think about when considering this kind of thing:
1) Mock exams, familiarisation, etc., are often about the parent's needs, not the child's (guilty
2) If the mock exam experience is challenging (which a CEM test might be) how will your child react to doing it all again a few weeks later? For some it can be helpful (i.e. the motivation aspect um talks about) but for others it can undermine confidence - and for our eldest, for example, performance in any situation is 80% about confidence and 20% about ability (0% about effort because there never is any).
3) Adrenaline can be helpful.
Saying all that, I put our son in for the BV exam (we did end up putting it on our form but we didn't intend to originally) and our daughter in for Warks. While they do mock SATS at school, so are used to taking tests to some extent, I don't think that adequately reflects the conditions of going somewhere you've never been before, taking a test of a type you've never seen before, surrounded by strangers.