Where It All Goes Down
Modern London
Sam's story goes down in England. He's just like us, really, except he's on the other side of the pond. That and he says, "mum" instead of "mom" and calls French fries "chips." Aside from this, Sam is just like any other teenager trying to navigate school, parents, and of course, chicks. The setting helps us understand why Sam uses a few different words every now and again, but it doesn't mean much otherwise.
We could see this plot unfolding pretty much anywhere from California to Germany. In fact, Sam even mentions in the book that teen pregnancy is an issue in a lot of countries in Europe. Perhaps that's his way of making sure his story is universal.