I used Derek for the PPL ground school and would recommend them; Claire does do the classroom teaching, except for the 'how an aeroplane and engine works' exam.
One or two subjects are taught during the day, and the exam sat in the evening.
I spent a week there and got through all the tests first time, and I arrived with some prior knowledge such as the aforementioned 'how an aeroplane and engine works'.
The week course is quite intensive, with long days, but to just get them passed and out the way prevents them dragging on over weeks at the flying club.
I found the teaching style good, with classes of 5 or 6, and I had an hours flying with Derek too.
Again, most enjoyable, I was very relaxed and came away with some good experience.
Any more questions, feel free to pm me.