Hi! I am no expert but your post popped up in new threads and I saw that you had had no answers, so I thought I should try to help.
From what I can tell, it is completely possible that children can be prepped using the DIY route - that is what we will go for, probably with some extra help here and there. The main thing is looking at the schools in your area to check which exam system they use. Once you know the type of exam the children sit, and the level of competition, you will know better what books/materials will be of help and where to concentrate your efforts.
Information about Surrey is here:http://www.elevenplusexams.co.uk/school ... ey-11-plus
The uncomfortable bit about the DIY route is that we, as parents, need to look at our own abilities and level of education to see if we could sit the exam ourselves. If we can't work at, or above, the level of the exam, then we need to find someone to help who can. This would not normally spring to mind, and I have no idea if this is of any significance, but you have a typo in your OP. If this is not immediately obvious you may need a bit more help than you initially hoped for...... Sorry to point that out but it is really relevant to your question about the DIY route so I hope you take it in the positive spirit which it is meant.
You might also do well to look in the Surrey Regional forum and read lots of the threads to pick up tips.
Good luck and hopefully someone who knows more about the Surrey are will be along soon!