Results on standardized tests are becoming a common way to evaluate student performance in different school systems, such as in different states of the United States. These tests are especially important in international comparisons of student performance since school systems differ so much across countries. International tests in mathematics, science, and reading have been given to high school students in different countries every few years since about 50 years ago. The well-know PISA tests started in 2000, and the number of countries included has been expanded by 2009 to over 60.
Scores on standardized tests have many well-discussed problems from the viewpoint of measuring how much students learn. For example, teachers may concentrate on materials that are likely to be on a test rather than on other possibly more important knowledge- this is called “teaching to the test”. Still, standardized tests are a much better way to compare achievements among students, and especially among students in different countries, than are various measures of average years of schooling- the most commonly used measures in international comparisons.