Catherine
You say that bright children at your child's school didn't get in because they weren't coached. But who said that they were bright? Their mother? Mothers often think they have given birth to a genius (

) - my wife thought that our daughter was the most beautiful girl in the world (come to think of it so do I), but may be you wouldn't agree? If your child is int he top group at school, it doesn't always mean that they are the cleverest in the class, it just relates to the abilities of the others in that class, but not necessarily those sitting the test at school. Unless you are the teacher at school, you don't really know.
I feel that the time that coaching really makes a difference, is when children are systematically coached by a prep school from an early age. This strikes me as unfair, but aren't the grammar schools concerned with this also, afterall, these private school kids must struggle once int he school?
You can do Times crossword everyday for 5 years and you may get better at it, but you may never be brilliant unless you already have the ability to do it (which I don't)