U.S. students persistently trail their international peers in mathematics achievement, performing particularly poorly on the application of mathematical concepts (Gonzalez et al., 2008; Organization for Economic Co-Operation and Development, 2009;Schmidt, 2012). This skills gap impedes U.S. economic growth and competitiveness (Goldin & Katz, 2008). Over the last several decades, U.S. schools have dramatically intensified high school mathematics curricula in an attempt to improve U.S. mathematics achievement (Domina & Saldana, 2012). Central to this movement is the effort to enroll a greater proportion of students in Algebra while they are in middle school. Algebra serves a crucial gatekeeping function in U.S. schools. For students who fail to master Algebra in eighth or ninth grade, the path to advanced training in mathematics and, subsequently, many well-paid and high-status careers is blocked (Adelman, 1999;Attewell & Domina, 2008; Long, Conger, & Iatorola, 2012). Furthermore, it is a uniquely challenging course, drawing heavily upon the concrete procedural skills that students develop in elementary mathematics and requiring students to develop a new set of abstract reasoning skills (