Yeah, I can second
Evolution Driving School. First year I did it I started with the 2-day phase 1 & 2, my times dropped dramatically as a result. It's all about car placement and being as early as possible. This year I did the phase 3, it wasn't as rewarding as it was more about data analysis than driving and the instructors couldn't find anything wrong with my technique. It's not cheap, but it is a good investment if you are serious about the sport.