After their 1969 inception as an electrical academy in a Philadelphia high school, the number of career academies grew steadily for two decades; since 1990, their growth has accelerated. Until the mid-1990s, they existed only as smaller units within high schools, but numerous high schools have since converted themselves entirely into career academies or other small learning communities. Career academies can be defined by these three basic features: they are small learning communities comprised of a cluster of students sharing some teachers and classes; they combine college-preparatory curriculum with a career theme, and they form employer partnerships. Fifteen years of California studies indicate that academy students outperform similar students in their schools in attendance, credits earned, grades, and graduation rates. Self selection casts doubt on evaluations of career academies. A random-assignment 10-site study confirms that students earn more credits and are more likely to participate in activities, but raises these two troubling issues: students in career academies score no higher on standardized tests, and teachers may be the schools' better ones. Career academies are compatible with major high school reform initiatives, including school-to-work, Coalition of Essential Schools, and small-schools movement. (YLB)