Schools are specifically banned from offering special coaching for the 11&divid; - any school that does is breaking the rules. I know a lot do!
Technically, no one should be coached for the exam - that way it's a level playing field and the children for whom the test was designed (bright children form disadvantaged backgrounds) have an equal chance of a grammar school place. In reality, this is not the case, and most grammar school places are taken by the children of middle class families who have the interest, the resources, the information and the ability to get thier children through the exam. (If you don't believe me, check out the level of free school meals at grammar schools compared to primary and high schools!)
Moving the exam to September will make this situation worse - some children will be coached throgh the summer, and the children who don't have that sort of family support will have to take the exam without even the extra term of teaching in Year 6 that they've had up to now.
There were children in my dd's class who were streets brighter than her, but she had the practice papers at home so knew what to do (no tutor, I am proud to say) and they didn't. She passed, they failed.
It is an iniquitous system.
Rant over.