One of the best things you could do for him is to help sharpen up ental mathsand vocabulary.
As for CDs do you mean theh interavctive CDs on this site?
The Tutors Cds for Verbal reasoning are relevant to Kent. You could try some of the free Demos and find out if your son likes them.
Games like Scrabble (using the distionary), boggle and word searches are also good. Keep a notebook of unfamiliar words and try some of Patricias compound word games
http://www.elevenplusexams.co.uk/pdf/11 ... tricia.pdf
There are some very good games on the internet for speeding up tables recollection.
Kent uses a multi choice format, papers set by Nfer so make sure that he gets practice in using the multiple choice answwer sheet.