Thinking aloud...
I successfully tutored my own dc for the 11+ and have been approached many times to tutor other people's children (I'm a teacher, but not at this level, but frankly didn't find it difficult to get on top of requirements for the 11+).
I've always said no to doing any paid tutoring (though I've tutored a friend's child for free) - I know I could make lots of money doing this but strongly believe that grammar schools should not only be open to the children of those who can pay - much like it used to be when I went to grammar school myself.
I'd like to return to that situation - where 11+ exams are NOT tutored for. But in the absence of that, I'd like to ensure that 11+ exams are open to everyone, rich or poor, and that the poor are as well prepared for the exams as the rich.
I'm happy to offer my expertise - but can't afford to spend my time tutoring everyone who might want it for free, personally.
So how to achieve that goal? I've thought of creating materials, websites... Anyone else like to join with me in this? Got any other ideas?