With only around a third of pupils getting 5 A*-C grades at GCSE, my state school was not good. It was put in to special measures around 2 years after I left.
I think if I had gone to an academically better school it might have changed my career path and most likely would have resulted in me doing something more conventional (graduate job, then working through the ranks etc). As it was, I started my own business and instead that has been more successful than I could have wished and wouldn't want to change that.
With all that in mind, I am pretty sure I will send my children to private school, at least for Primary. We are lucky enough in the area to have Grammar schools which have results at least as good as an average private school, if not better.