A decade ago, most Seattle-area high schools offered just a handful of rigorous classes that provided a way to earn college credit while supercharging a transcript. And only students with top grades were allowed to sign up. But in 10 years, the intensive, fast-paced Advanced Placement (AP) classes have skyrocketed in this state. In 2008, fully one-quarter of Washington public-school seniors took at least one AP test during their high-school years, compared with 10 percent in 1997. In some schools, almost every student takes an AP class in junior or senior year.