PREFACE The Third International Mathematics and Science Study (TIMSS), sponsored by the International Association for the Evaluation of Educational Achievement (lEA) and the gov­ ernments of the participating countries, is a comparative study of education in mathematics and the sciences conducted in approximately 50 educational systems on five continents. The goal of TIMSS is to measure student achievement in mathematics and science in participating countries and to assess some of the curricular and classroom factors that influence student learning in these subjects. The study will provide educators and policy makers with an unparalleled and multidimensional perspective on mathematics and science curricula; their implementation; the nature of student performance in mathematics and science; and the social, economic, and educational context in which these occur. TIMSS focuses on student learning and achievement in mathematics and science at three different age levels, or populations. • Population 1 is defined as all students enrolled in the two adjacent grades that contain the largest proportion of 9-year-old students; • Population 2 is defined as all students enrolled in the two adjacent grades that contain the largest proportion of 13-year-old students; and • Population 3 is defined as all students in their final year of secondary education, includ­ ing students in vocational education programs. In addition, Population 3 has two "specialist" subpopulations: students taking advanced courses in mathematics (mathematics specialists), and students taking advanced courses in physics (science specialists).