Since the publication of "A Nation at Risk", ACT has recommended that students take a core curriculum in high school in order to be prepared for college-level work. ACT's recommended core curriculum consists of four years of English and three years each of mathematics, science, and social studies. The benefits to students of taking the right number of core preparatory courses in high school have been well documented by ACT research. More recently, ACT research has also shown that taking certain specific courses in high school, such as Biology, Chemistry, Physics, and mathematics courses including Algebra II and beyond, substantially increases students' readiness for college-level work as well as their readiness for workforce training programs. The purpose of this brief is to summarize ACT's research on the core curriculum. It describes the relative benefits of taking the ACT-recommended core curriculum, and of taking specific high school courses. The brief is divided into two parts: benefits for academic achievement and college and workforce training readiness, and benefits for college success. Unless otherwise specified, the results reported here are based on the 2005 ACT-tested high school graduating class, totaling about 1.2 million students. Of these students, 56 percent took the core curriculum and 34 percent took less than the core curriculum. (Contains 14 notes.)