Some info on standardization is on this very forum.http://www.elevenplusexams.co.uk/advice ... xplanation
There is link at end of that webpage, where you can read more on NFER site.
We are doing DIY mostly. We did DIY in the begining, then had a tutor (peer pressure), then now again on DIY. Last month, DC sat for Sutton mocks. Additionally, we plan to take 2 mock tests. I will pm you if you want more details.
By now, I think you would have already covered for VR/NVR techniques and practice.
For VR, we followed Patricia's advise. I will search and post the link to you. It is the sticky post on Bucks forum. Very useful advice.
For NVR, we did Bond assessment books upto 5, followed by AE and Learning together and now would go to GL test papers from early August.
I know most children go to tutors. If tutor is good then that is helpful, otherwise it is like expensive babysitting. However, you do get an idea about peer performance and some competitive spirit.
In our experience, we found DIY more useful. As your child is bright and self-motivated, I am sure he will sail through. Good luck.