Researchers have done a mind boggling number of studies into what makes a good school, from whether single sex schools are any better than co-ed (apparently it makes no difference) to whether it's a good idea for gifted kids to skip a year (the answer is a resounding yes). In this book, Gillespie goes through a range of topics like this and provides a review of the research.
One thing we learn is that education is a difficult area to research. It's hard to design a study that isolates the exact variable you're trying to measure, hence there are often thousands of studies on each topic that reach a broad range of opposing conclusions. This is where we rely on Gillespie to navigate us through the mess of conflicting findings. Unfortunately, on the main question of whether private schools provide value for money, he reveals that he had already made up his mind before doing the research, and I came away unconvinced by his opinion that private schools are a total waste of money.
Even so, I think this sort of book is a valuable contribution to public debate and there is enough here that you're guaranteed to learn something interesting that will inform your decision on choosing a school for your kids.