I bought this book to tutor a GCSE student who was covering the American West (I hadn't) and was able to read and absorb it in about a week, but I'm a graduate in my 20s, which makes it a lot easier than it was in my teens. It's a solid, comprehensive and (fairly) unbiased review of the period with a good number of sources and case-studies. Personally I'd read it for pleasure, I thought it was really interesting, but it also offers enough information to pull out an A* at GCSE (or whatever they're handing the kids these days).
I can thoroughly recommend this book either for current GCSE students or anyone who wants to understand a fairly substantial chunk of the current world super-power's admittedly brief history.