agree with dixie, there is a lot in the maths that isn't necessarily taught in year 5.
and yes, mine all coasted through year 6 and SATs having prepped for 11+
The phrase - if you have to do all that work/tutoring for 11+ then maybe they shouldn't be there is really misleading.
Take my student this year. Very intelligent, easily of grammar standard, and there is one school which is sort of super, super selective, and I expect her to pass for it.
She certainly didn't need weekly tutoring, but had she had no prep at all, I don't think she would pass. She had never seen any Non verbal reasoning, and needed some practice on that. She had never seen the answer sheets and got it wrong the first time.
Her maths is amazing, but there are lots of maths facts that she has learnt so that she can recall then very quickly
(eg, internal angles of a triangle add up to 180, definition of correct terminology eg prime/factor)
She hasn't been tutored up to the test, she has been made ready for the test. There is a difference. And in these days where everyone is prepped in some way, I do think it is necessary. It is, for most, their first experience of any sort of formal exam.
Also, if you are in a grammar area, eg Kent, they take about 25%/30% of kids into grammar schools. In our area it is about 5%. But we have fewer kids per lace than in some of those London boroughs where the competition is very stiff. Also, some areas the tests is taken as part of the school day, but for us you have to travel to the grammar school and sit it there on a Sat, much more intimidating.
And yes I am a tutor, but the first thing I say to parents is that they don't need me, they coudl do it them selves and show them how, but they prefer to have me to it.