My DD is a year ahead of your DS, and is about to sit the 11 plus for the Birmingham area. We've not had a tutor, and she's at an ordinary state primary that is not pushy at all, so they have not gone ahead of the curriculum. She has done workbooks for the past year, probably averaging an hour per week for the first two terms, and stepping up a little in the past couple of months.
Obviously, I don't know what the actual test will be like, but I think she's quite well prepared. We started with age 9-10 workbooks (actually, 8-9 for non-verbal reasoning, as it was completely new) and worked up to 10-11. We used a range of publishers: CGP, Bond, Schofield & Sims, Collins, First Past the Post.
The CGP books are very good, clearly laid out and methodical. DD started with the 11 plus books at 9-10 which took you through the sub-topics one by one, and if there was anything new or tricky, we did some more practice with the help of the internet, so DD learned as she went on. She would have been daunted by that Bond paper a year ago!
She has also done a couple of mock tests locally, which mimic the exam format and atmosphere. I think these were really helpful, but one or two would be enough.