1st: As you may already know, Tiffin tests uses " NEFER NELSON" version on both VR and NVR. So, make sure your DS is familiar with its "style". Yes, it is harder than the rest version, such as AFN, ect.
2nd: I personally found the book " How to do Non-Verbal Reasoning" by Bond Assenssent Papers helped. It is a step -by -step guide to all the different types of questions commomly set in non-verbal reasoning tests to 11+ exams. There are 45 types of questions al together. ( Yellow Cover)
Meanwhile, I send a PM to a friend of mine whose son took and passed both Langly and Tiffin exams last year. If my friend is in the UK now, hopefully , she will give you more support?
Oh, my fellow Tiffinian parents: please don't be panic. The test on the Dec 9th: your DS won't feel intimidated if he knows Nefer Nelson questions well enough like his Yu-Gi-Oh cards. My DS is just an average boy in term of academic study and far from super intellgent. If he made it, everyone gets chance to make it. Let's sing together now: " Bob Tiffin Builder, can we make it? Yes, we can! Yes, we can!"