Hi @evtheria 👋 welcome aboard. Is it state grammar you're looking at? If so then a look at the 11 plus forums and scroll down to find the section for your county will give you some insight into the sort of prep and expectations and experiences of others in your area, I've found it a really useful place to stalk! Most useful for me the last couple of times have been the threads where people post scores and offers, as you really get an idea of what you need.
If you're looking at private schools with 11+ , so selective private rather than grammar, then I know very little but others will know more and I can't imagine the prep period is that dissimilar. We're looking at 2 state grammars only, the test my DS will sit could get him into the running for 4 , and for 2 of those the marks wouldn't actually need to be as high as the ones we're trying for, but they are just too far across the county to be a consideration.
We are definitely doing some prep, but trying to keep it relaxed and in short bursts. My own view is if you have to really cram then your child may not be happy in that school anyway, but I do see that some tutoring (whether with a tutor or diy) is needed due to the ridiculous level of these tests now, especially the super selectives where we are. We've just allowed ourselves to be guided by our kids. DC1 wanted it and you could really tell. DC2 only wanted 1 of the 2 schools we wanted, flatly refused to even consider the other (took a dislike on open day) so we didn't even put it on our firm in the end, thankfully he got the one he tried for! Final DC is currently quite keen and working to try, but I shall see how he feels when we look round. He knows that we won't force him into a grammar at all costs, (impossible anyway as they could just go into the test day and not try) it's got to feel right. So I guess we encourage them to work for it, understanding that not all kids will just do that off their own initiative, we do have to say come it's time to do 15 mins maths or whatever, but if I'm getting strong resistance I back away. If I was getting strong resistance more than not, I think that would tell me it wasn't right in any case.
Sorry, I've really rambled on, I hope that was in someway useful, feel free to ignore if not!